Why China actively has opposed deployment of thaad on South Korea? Why the U.S. has kept to install thaad on South Korea? What could be the choice of the new South Korean government under the pressures of the U.S. and China? This paper attempts to answer the questions mentioned above. The results of the research show that Thaad is the key weaponry system for 'All Domain Access Strategy' that the U.S. has adopted to make 'rebalance' against China. The Thaad could undermine the 'Anti-Access/Area Denial Strategy' that China has pursued to prevent Chinese “core interest” areas from the U.S. intervention. Thus, Thaad is the critical weaponry system for the U.S. to check Chinese military capabilities. Conversely, China is hard to reduce asymmetrical military capabilities against the U.S. because the functions of Thaad. Since if Thaad is deployed in Korea, there could be ‘big’ advantage for the U.S. military strategy but ‘huge’ disadvantage for Chinese military strategy. In that sense, both the U.S. and China can not yield their own position with regard to the deployment of Thaad on South Korea.