Hi Mingsoul,
For PNS camera for diving, do get camera that allow you to adjust manual white balance. Most casual underwater photographer tend to take more macro shots then wide angle for obvious reason. So do consider the minimum focus length as well. You will also need to factor in the cost of the underwater casing on top of the camera. Canon use to produce good powershot A series camera that is relatively cheap and good for diving but I am not too sure now.