Abstract: After Chinese People’s Volunteer Army returned to China, Democratic People’s Republic of Korea (DPRK) took this opportunity to initiate the peaceful unification of the peninsula, aiming to alleviate its tension with the U.S. However, the U.S. implemented the policy of “hostility, restriction and non-contact” in its “asymmetric relationship” with DPRK, gave up the peaceful unification of DPRK guided by South Korea, maintained the separation of the peninsula and handicapped the development of DPRK by strengthening the power of South Korea. This brought a serious crisis to Korea Peninsula in middle-late 1960s. Especially, due to Johnson Administration’s promotion of the normalization of the relations between South Korea and Japan, the alliance of the U.S., Japan and South Korea made a considerable threat to the national security of DPRK. In addition, Kim Il Sung attempted to unify the peninsula in a way of Vietnamese Reform. As a result, constant mild conflicts occurred between DPRK and South Korea and the tension in the peninsula was intensified. However, the U.S. excerted contradictory policies: on the one hand, it prevented South Korea from attacking DPRK for the stability of the peninsula because of its involvement in Vietnamese War; on the other hand, it increased to a great extent its military aids to South Korea, which intensified the rivalry of South Korea objectively. Therefore, the alliance of the U.S. and South Korea was a great hindrance that prevented the alleviation of the crisis of Korea Peninsula. The U.S. had limited choice when handling the crisis, so it was inevitable that its policies towards the peninsula came into a dilemma.