am staying in china... i want to go hong kong for visit, so how can i get visa for HK from mainland.

Ananta, you go there for sightseeing purpose, right? If yes, you should first prepare the required documents including the filled-out application form attached with a passport-style photo, your passport and copy of its data page, proof of your financial support, your residence permit in PRC, transportation arrangement and your travel itinerary to HK. Next, submit your application to Beijing Office of HK SAR government to apply for it.