I'm a Malaysia. My China Visa expire on 23/09/13. Can i enter China to Tibet on 02/09/13.

Yes, you can enter China before it expires. You need to apply for a Tibetan Travel Permit from the travel agency in order to travel in Tibet. Usually, a group of 5 to 6 people of the same nationality might get the permit. Besides, I am afraid that you need to join a group tour because individual foreigners are not allowed to enter Tibet.