I'm a Sri Lankan citizen. my wife is a Chinese. how I can get long term visa to go and stay China?

Saleeth, you can apply for a Q1 type at the PRC embassy. The first step is to prepare all materials that may be required, such as: 1. Original passport with at least six months of remaining validity and blank pages, and a photocopy of the passport's data page; 2. One completed Application Form with a recently-taken color passport photo (bare-head, full face) against a light background attached; 3. An invitation letter issued by your wife; 4. Photocopy of your wife's ID card; and 5. Original and photocopy of your marriage certificate. Next, submit the application to the embassy.

With the Q1 type, you can get a residence permit of PRC, which allows you to stay for one year or so. Then you can renew your residence permit one month before the expiry date to stay for a new year.