After the cold war, there are obvious adjustment and change in the field of South Korean diplomacy with the dissolution of the Cold War system and the rise of China. The most prominent feature of diplomacy in Northeast Asia from Roh Tae-woo to Roh Moo-hyun is to break away from U.S and Japan reasonably and be friendly with China. However, the conservative government of Lee Myung-bak blindly followed the hard line policy of U.S, and held a series of massive military maneuvers aimed at North Korea while applying economic sanction, which made a reverse in North and South Korea relations and armed conflict. So the situation in Northeast Asia became sharpened and the relation of China and South Korea got certain damage. At present, the sudden death of Kim Jong-il brought a new change in the situation on the Korean Peninsula. Especially on the background of global strategic focus speeds up towards the east, diplomacy of South Korea in Northeast Asia is in a dilemma in whether strengthen U.S-Korean alliance or promoting strategic cooperation relations. Diplomacy intelligence of South Korea will be tested by reality.