So I've had this guy for over 10 years, since both I and him was very small xD. I don't know what is he. He lives in water almost all the time and eat almost everything, I feed him with live fish(lots of live fish in the pond but he doesn't like fish anymore), vegetable, fish food, raw meat(rarely). Is there any other good food I can feed him?
Definitely a soft-shelled turtle. Possibly the Chinese Soft-Shelled Turtle (Pelodiscus sinensis). They get to about a foot long, and are the most commonly seen soft-shelled turtle in the hobby AFAIK.
Wikipedia says they eat crustaceans, molluscs, insects and fish at night. You could try cockles, shrimp, strips of white fish, etc. Soft-shell will take small mammals and birds, and the largest have been known to attack goats.
I've never seen a turtle catching a pray... I can't even imagine how mine was able to catch a rat. area near my pond was a good place for rat, as it's close to the sewer and lots of hiding place. But about 4 years ago, I've discovered dead and half-eaten rats in my pond