Simple and Direct:
* I am half Chinese and half English.
* I am half Chinese, half English.
* I am half Chinese and half British. (If you want to specify the nationality)
More Descriptive:
* My mother is Chinese and my father is English.
* I have Chinese and English heritage.
* I am of mixed Chinese and English ancestry.
* I am bicultural, with both Chinese and English roots.
More Casual:
* I'm a mix of Chinese and English.
* I'm half Chinese, half English.
The best way to say it depends on the context and who you are talking to.