Can i visit my friend at shenzen as my long vacation holidays?

You can visit him after you get a proper visa. For a L type one, you need to provide:
1. passport with at least two blank pages and a validity of six months.
2. completed application form affixed with a recent passport size photo.
3. invitation letter with an official seal, authorized signature and contact details from a host company or travel bureau in China which enjoys legal person status and must be registered in China. The invitation should be attached with an envelope postmarked by Chinese Post Office
4. flight and hotel reservation
5. proof of economic guarantee, both original and copy version