I am not good at writing, there maybe something wrong in my comments. Anyway, just give my best shot.
Many countries are composed of different ethnic groups;(I guess the punctuation here should be a full stop.) for example, there are fifty-six ethnic groups with various cultures in China. Whether multi-culture is beneficial or detrimental has not reached the consensus. In my essay, I will argue that though there exist some problems in multi-cultural societies, there are still more benefits to a country and its people.
Indeed, multi-culture in a county can cause (I'd like to change into led to) several problems with social harmony. First of all, different cultures are always accompanied by culture clash. People in different ethnic groups usually do not agree with each others belief and moral values. Because of this, another detriment occurs that the whole society becomes less stable and harmonious, which can impede the development of society. The last point is that it is more difficult for the authorities to govern the country due to (due to is incorrect use here, just change to because) different ways of life and religious faith in different ethnic groups. (Actually, why not just write different ethnic groups have different life styles and religious faith)
Despite the disadvantages (the disadvantages of what?) , however, the society as well as (I guess and is okay) the citizens can obtain more benefits from multi-culture. Different ethnic groups can learn from each other because each culture has its own advantages and disadvantages. This can enrich the country’s culture. Another point is that the artists can get many new and stimulating inspirations from other ethnic groups’ culture. Multi-culture provides artists with plenty of sources for to their art creations. In addition, since different ethnic groups have their own distinct forms of art, such as the distinct songs, dances and musical instruments. The citizens can entertain themselves with and appreciate the exotic forms of entertainments.
In conclusion, multi-culture can not only bring benefits but also cause some problems in a country, but I believe that there are more benefits than drawbacks to a country provided that the government can cope well with the cultural clash and respect each ethnic group’s culture.
The last paragraph is not good, you even don't tell me what's the advantages and disadvantages, we need the specific conntent. There are some punctuation problems in your essay. Mostly, it should be a full stop but you use comma. Especifically in the last paragraph.
The are also plenty of tired, overdue and meaningless phrases in your essay. Such as "disanvantages ad advantages", "In addtion", "firstly", "another point is that". Do you get my points? Yep, admittedly, some books in China is good, like the book of Pat. BUT it is overused. I found that so many people use the same style of words in their essays. Just imagine what the examiner would think when they evaluate your work. I had the same problems with you, and I think we should get rid of that book. The word is good inside, HOWEVER, the conjunction in his book screw our essays.
The sentences is a bit long, the average words in your sentence is 20.4. Cut it off, there is no need to write that long.
Your grammar is good, you rarely make mistakes in your essay. The content is good, I can get your point inside.
Hope you can achieve good score in your Ielts exam.