my clothes iwant send from guangzhou to kuwait by bag weight 25kg how much total RMB

Sorry to tell that each package sent from China to Kuwait should be no more than 10kg, so you nee dto send them separately. Then by air mail, the fare is 736.80RMB/10kg and 413.80RMB/5kg, excluding insurance and other fees.

It is hard to tell you a proper branch of China Post office without your current location. But you'd better find a relatively large one, because some small sites don't send international packages!