Since 2015，we see an endless rumors of secret negotiations on deploying “THAAD” anti-missile system between the ROK and the USA，especially after the ROK chose to join China’s leading and building the AIIB in March，the attitudes of the ROK and the USA governments on deploying “THAAD” anti-missile system within the territory of the ROK are different several times. Its reasons are not only the USA’s political motives and military intentions，but also the ROK planning to deploy “THAAD” anti-missile system. But for the ROK，although “THAAD” anti-missile system can make up for the inadequacy of the Korean national missile defense system，but also faced with many challenges and resistance. The ROK should treat the deployment “THAAD” anti-missile system with caution，make the right strategic choice.