The article attempts to analyze China’s Korea policy through a game theory. A game-theoretic explanation assumes that China is a rational actor; China behaves rationally to achieve its national goals, whatever is, by calculating the cost and benefit of its moves. Currently, China’s top national goal is “a wealthy people and a powerful country.” To meet this, China keeps relatively contrasting grand strategies; one is a strategy of peaceful rise(heping jueqi) and the other is a strategy of “do things to be done(yousuo zuowei).” China’s bilateral relations with states concerning the Korean peninsula results from the logic of these two grand strategies. China’s relations with the United States has a payoff of the prisoner’s dilemma game. For the stability of the Korean peninsula, China takes a cooperative strategy toward the US. By contrast, China attempts to discourage America’s China bashing by supporting its ally North Korea. China’s relations with North Korea can be called a spoiled child game. Given North Korea’s geopolitical significance, China has no other choices but to appease North Korea with massive assistance, politically or economically. China’s relations with South Korea is same as its relations with the US, the prisoner’s dilemma, but the difference is the current China-US relations is in the Pareto optimality(mutual cooperation) and China-South Korea relations is getting into the Nash equilibrium(mutual defection). To dissolve recent tension the relations with China surrounding the Cheonan Ship Sinking and Yeonpyeong Island Attack, South Korea needs to reconsider its excessive pro-American diplomacy which might estrange China.