The freedom of expressing ideas is crucial for the prosperous of arts.   there is not a further discussion with this topic sentence.

so i feel your para2 is not very logical.

but you are great to use some very difficult words. such as: pornographic, proliferation, prosperous, censor, liberal, bureaucracy.   i will learn them

There are very few things here I would change. Your word count is 264, which is fine. With a difficult abstract topic, it may be hard to reduce sentence length, but you should still try. Add some short (4-8 word) sentences to reduce your average from 18. 5, which is a little too high, down to about 15.

Apart from the few word choice and usage errors below, there’s not really much I would change!

Word Choice/Word Form/Usage

• expressing ideas is crucial for the prosperous of arts → expressing ideas is crucial for arts to prosper/thrive    OR for the success/survival of art
   
• The appearance of profound and touching works would be hard to imagine if…→ It would be very difficult for profound or inspiring works to appear if…
   
• Moreover, the arts with pornographic or violent contents are… → Moreover, art with pornographic or violent content is
   
• Teenagers' access to these fictions and films should also be regulated → Teenagers' access to such artworks should also be regulated by the government. 
   
• The freedom of expression is imperative for the prosperous of arts → The freedom of expression is imperative for the success of the arts

Punctuation

The appearance of profound and touching works would be hard to imagine, if the government prohibits the artists from describing the pains of common people, or forces them to exaggerate the contributions of the bureaucracy. 

No comma after ‘imagine.’

What band do you think this essay would get? Have a look at the official descriptors for IELTS Task 2 Writing (public version) here, to estimate what the grade would be under each heading. 

In China all kinds of arts (literary work, films, music, etc.) are strictly censored by the government, in order to prevent the proliferation of any arts that run contrary to the principles of "socialism". Some liberals assert that artists should be able to express their own ideas freely. As far as I am concerned, government regulation should be limited in the arts field.

The freedom of expressing ideas is crucial for the prosperous of arts. The appearance of profound and touching works would be hard to imagine, if the government prohibits the artists from describing the pains of common people, or forces them to exaggerate the contributions of the bureaucracy. Artists should be able to let their imaginations soar, without being penalized by possible imprisonment, so as to create great art that has the power of suggesting a world beyond. 

But we can not assume that artists should enjoy the freedom to do whatever they want without any regulation. Some artists are interested in extremely weird forms of art, which may run contrary to social ethics, or even violate the law. Any criminals should be punished, regardless of the career. Moreover, the arts with pornographic or violent contents are unfit for the teenagers to view. Teenagers' access to these fictions and films should also be regulated by the government. 

Overall, government should not interfere with the artists' actions, as long as they comply with the law. The freedom of expression is imperative for the prosperous of arts, and government meddling would only stifle the creativity of visionary and illustrious artists.