If you want to improve your english I do not believe that it would make a lot of difference in half a year by going abroad. If I were you I would rather stay in China to do the same thing. This way it would be more effective and efficient.
However, if you have determined to do so by whatever reason, you can try to apply for a visitor visa, which can allow you to stay in UK for half a year maximum. There might be some difficulties if you do not have anyone you are familiar with here.
Good luck.
