Do i need a VISA transit on Vancouver if i take fight from US to Vancouver to CHINA?

I think you may get free transit in Vancouver if you meet the following requirements
1. holding valid Chinese passport
2. holding valid USA visa
3. taking a flight from Air Canada, Jazz Aviation LP, Cathay Pacific, China Airlines, Philippines Airlines or Air China
4. transit at terminal 1 of Vancouver Airport

If you don't meet the requirements or you are worried that you might be refused for a free transit, then you should apply for a G type from Canadian embassy in USA before you go.