I didn't make it!
How can i kill the dragon (khao kai) or something like that???
Which one? (and you mean the Pao Kai :P)
Well, the first one you encounter, lure it towards you by shooting at it with either magic or arrows and then when you have its attention run back into those portcullis's. Then it ought to stick it's head through. Pull the lever, drop the gate on it's head. It's not that hard :P.
Or in the other one you blow it away with your gigantic crossbow machine xD