There has been heated debate between China and South Korea over the issue of THAAD deployment in ROK. From the standpoint of China, the deployment is a major issue which concerning the global strategic balance. It seems to China that the THAAD deployment will do nothing to solve the nuclear issue of north Korea,and it is beyond the South Korean defense needs. Moreover, it has seriously threatened China's security interest, undermined Sino-ROK relations and the trust between the big powers. The issue’s essence is the promotion of US deploying global anti missile system. For that ,China and Russia jointly defend the THAAD has become an inevitable trend. The Improvement of Sino-ROK relationship focus on the the national interest and prospects for denuclearization of the Korean peninsula. It means that the two sides have not changed their positions, and the THAAD problem has not really been turned over.