This is the official site of the government of the People's Republic of China, for statistical data pertaining to that country. It is the most valid information source for economic, demographic and other quantitative measures.
This site is sometimes unavailable, and throws "Server busy" errors, so it has much lower vendor reliability than most other comparable sites from other governments. Similarly, data is not as current as comparable sites from other countries.
N.B. My comment is not intended as a contradiction of this: http://www.mywot.com/en/scorecard/stats.gov.cn/comment-5907213