Thanks everyone for the warmest welcome i have ever had on internet forums =)
Dr.Bill, Hainan is the most popular diving place in China, i have never been but heard it is not so nice there. Damaged corals, few fishes and bad management. That's what i heard, i cant really judge that.
Some divers have gone to Dongsha and Xisha Island in the Southern China sea, it's a kinda new spot and not easy to go there since no operator is really doing the business in those areas, but we can always rent a fish boat or sth and go there, which is quite a lot of hassel.
Besides shenzhe, Zhuhai is nice for diving, probably better than Shenzhen, Hongkong also has some diving spots. Generally, i prefer going out to dive and do some travellin for 2 weeks or more.