today when I washing my car, there's little bit water laking into my exhaust, after I done start the engine, the sounds like little diffrent, so its very big problem? or I just have to wait till the exhaust dry?

 

No, water up the ol' exhaust won't hurt at all. It'll just get blown back out by the current of exhaust after you start your car. I've seen little kids shoot water into the muffler of a car when they "helped" wash the car before, TONS of water, and it just trickled out after the car was started.
The only problem you might have is rust from the inside out.

 

condensation :-/

 

If you have a chambered muffler then there's some chance of water damage.

Your car would have to be half submerged in a lake to cause engine damage.