Thanks -  this rewrite of your introduction is much better because it has the keywords (or topic, or synoynms) directly in the first sentence. 

Here are a couple of tiny errors tidied up and to make every sentence relevant. I've also removed some repetition:

Humans do not just depend on animals and plants as their major sources of food. We also depend on them to retain a balanced ecology in this world. However, a large number of animals and plants are endangered or threatened with extinction worldwide. This essay will discuss the major causes of wildlife extinction and some preventive/preventative steps that need to be taken to safeguard our animals and plants.  

Human not just depend on animals and plants as their major sources of food. We also depend on them to retain our balanced ecology system in this world. However, large number of animals and plants are threatened with extinction these day. Number of endangered species keep increasing from time to time throughout the globe. This essay will discuss what are the major cause of this issue and some prevention steps that need to be taken to combat the problem.  

I didn't look at the comments before I wrote mine and I'm sorry now. Chenyu Lue wrote:

I think the introduction should be shortened. The background introduction should be related to the topic, so I think the first two sentences could be canceled. Besides, the last sentence should be the topic sentence telling readers what you are going to talk about.

Absolutely correct and well spotted! Great advice!

However, I'm happy with Ammat's topic sentence ('Human activity is the main cause') -  I think this is OK because it covers pollution AND hunting AND habitat destruction. 

In short, Ammat, the essay is fine -  just work on your intro and try not to do fluffy or vague! Make every sentence count. Well done, and thanks again to everyone for their comments. 

Introduction

This is the weakest part of your essay.

• Deterioration of ecosystem will give a negative impacts to the world such as landslides, climate change and floods

There are eight nouns in this sentence. We could change some to adjectives and replace some with verbs. However, what does the sentence really say?

• The world has environmental problems.
• Landslides, climate change and floods are major environmental problems.
• Our environment is changing. We now have more X, Y and Z.

You could leave it out completely, or put it in the body. There's a bigger problem, however, apart from its vagueness. It’s off-topic (see the word ‘tangential’ in Task Response in the official descriptors for IELTS Task 2 Writing (public version).  

Your essay really starts at the third sentence. Get to the point quickly. Mention the topic in the first sentence. Animals, plants  - work them in.

A balanced ecosystem is an essential need for a better tomorrow for mankind. Deterioration of ecosystem will give a negative impacts to the world such as landslides, climate change and floods. However, large number of animals and plants are threatened with extinction these days. We depend on them not just to have our daily food but in many ways especially in environmental and ecology control. So that, causes and preventions steps should be taken into account before it become worse.

 What’s the difference between ‘environmental’ and ‘ecology’?  What does ‘in environmental and ecology control’ mean?  Could you specify?

Thesis sentence

You don’t have one. You need one. A thesis sentence helps the reader to know what is coming in your essay. It reminds you of how your essay will be laid out, and it makes it very easy for the examiner to give you a good mark for Coherence and Cohesion (see “presents a clear central topic within each paragraph”) in the descriptors.

This is not a good thesis sentence:

So that, causes and preventions steps should be taken into account before it become worse.

It could be used in a million essays. What does ‘it’ refer to? What are the causes? What are the steps? Why not specify? Where are the keywords (‘animal’, ‘plants’)? Here’s one possible rewrite:

This essay suggests that human activity is the main cause. It also points out we need to stop hunting and polluting and instead educate our children about protecting wildlife.

Word Choice/Word Form/Usage

• So that, those plants and animals cannot survive → Because of that, many plants and animals cannot survive

The body of your essay is fine. Good!

The last sentence in your conclusion needs work. You wrote:

This the only way for us to have a better tomorrow for our next generation.

Yes, it’s nice, but examiners will ignore it. It’s not directly relevant to the topic. It could fit into many essays, perhaps not a million, but several thousand.

Where are the animals? Where are the birds and the plants and the forests?  Make sure every sentence is relevant to the topic. It's a test of how you can answer the question, not how many nice phrases and sentences you can produce at random!

yes I have followed the sites that are suggested by MR. Writefix like dc ielts and ielts-blog. And one of my friend adviced me to look upon ielts-simon. According to my experience, you can gain a lot of knowledge from these sites but what you really need to do is practice a lot and submit your essay to the one who will correct your essay. Even if you had no teacher then you can do it yourself by the way our respected sir writefix had been saying that is none other than by using MS Word with its word count. It also really helps a lot. I had improved a lot and you can also feel the difference after some duration of consistent practice when you compare your recent and past essays. Believe me the only magic wand is hard work and practice. Take your time and put on your effort you will surely win the race sooner or later.

Best of luck to both of us.

Essays.

Hi essays...

yup...i need more practice then.Huu.BTW, can u suggest some website/blog to me?

I read your essay. I think you are new to ielts. So, these kind of mistakes do occur when we begin to write essays at the initials and I completely agree with the mistakes that had been pointed out by our member friend chenyulue. However, what I like to suggest you is go through some of the band 7 or higher essays sample, you will obviously draw out that there are similar answering pattern to most of the questions. like, agree/disagree, problem/solutions, opinion/discussion. In this way, you can learn some of the key words as well which you can automatically apply on some of your writing, but what you need to expand is your ideas about the various topics. I am really impressed with the various ideas you had presented in this essays but you lack the presentation which you surely will improve with a lot of hardship. So, keep on practicing. There are various ways of practicing either writing in MS word, taking a private tutor and in my view this site is also quite a lot helpful for improving your writing skill.

Best of luck.

Essays!!

A balanced ecosystem is an essential need for a better tomorrow for mankind. Deterioration of ecosystem will give a negative impacts to the world such as landslides, climate change and floods. However, large number of animals and plants are threatened with extinction these days. We depend on them not just to have our daily food but in many ways especially in environmental and ecology control. So that, causes and preventions steps should be taken into account before it become worse.

【I think the introduction should be shorten. The background introduction should be related to the topic, so I think the first two sentences could be canceled. Besides, the last sentence should be the topic sentence telling readers what you are going to talk about. One possible introduction could be " Humanity cannot live without plants and animals since they provide us with our daily food, but the deteriorating ecosystem and human activities which have encroached upon the survival of the creatures in nature have endangered many fauna and flora. This essay will examine the causes of the problems and suggest several solutions to save these endangered animals and plants."】

      【Add a central topic sentence, such as "The danger of extinction is the result of several important factors."】It is true that h Human activity is the major cause of this problem. Urban D development of cities with construction of buildings and skycrappers will destroy animal and plant habitats←【This sentence has some grammar errors, please check it】. Therefore So that, those plants and animals cannot survive because their food sources, home and breeding to new generation has been disrupted. Another significant cause is the hunting of rare species for exotic food and traditional medicines which can be sold at high prices. In addition, pollution of air and water can interrupt plants and animals life. For example, pollution of sea can threaten plankton and coral life which is a source of food and shelters to oher marine life.

I mainly make some corrections in the first two paragraph, some of which may be not proper, but there are still some basic grammar and spelling problems in another two paragraphs. You can check and correct them in MS Word. 

A balanced ecosystem is an essential need for a better tomorrow for mankind. Deterioration of ecosystem will give a negative impacts to the world such as landslides, climate change and floods. However, large number of animals and plants are threatened with extinction these days. We depend on them not just to have our daily food but in many ways especially in environmental and ecology control. So that, causes and preventions steps should be taken into account before it become worse.

      It is true that human activity is the major cause of this problem. Development of cities with construction of buildings and skycrappers will destroy animal and plant habitats. So that, those plants and animals cannot survive because their food sources home and breeding to new generation has been disrupted. Another significant cause is the hunting of rare species for exotic food and traditional medicines which can be sold at high prices. In addition pollution of air and water can interrupt plants and animals life. For example, pollution of sea can threaten plankton and coral life which is a source of food and shelters to oher marine life.

       A number of urgent measures need to be taken in order to solve this problem. Firstly, the hunting of rare species should be banned and international agency to be set up to prevent the illegal trade  of these animals.Apart from that, government and local council can apply dome rules and regulations about pollution of river, sea and air against irresponsible companies and individuals. Heavy fines can be imposed to those who are against the laws. In addition, the public and children must be educated with knowledge about the importance of environment and ecosystem surround them. This can be done through campaigns in public and syllabus in the school.

       In conclusion. this problem will remained unsolved if we do not work hand in hand with other parties such as government and conservationist. people should be tolerant with each other and care about their surroundings in this world. It includes animals and plants on the earth. This the only way for us to have a better tomorrow for our next generation.