I need to stay for 7 days how can apply the visa?

You need to prepare the following documents:
1. finished ID1003A form
2. a recent passport photo
3. flight itineraries and accommodation booking in HK
4. financial proof, recent six months bank statement, pay slip or employment certificate

If Chinese embassy deals with your application, it takes 4 working days. If your application was sent to HK Immigration Department, then you need to wait four to six weeks.