This research adopts the historical approach to analyze the causal relations between the cooperation of KMT and CCP and Taiwan’s China policy. The study of essential historical and academic documents provides the main resources of the research projects. The conclusion of this research is that: Taiwan’s China policy, no matter under the domain of KMT or DDP, is deeply influenced by the status of cooperation between KMT and CCP. So far there are three times of cooperation between KMT and CCP happened in history. The previous two happened before World War II, when KMT still controlled the regime of China. The third time happened when KMT became the opposite party and DDP came into power. All these experiences of cooperation between KMT and CCP had causal effect on KMT and DDP, though the level of influence might be different. The discourse created by the cooperation between KMT and CCP also had impacted the DDP when it was in the office since 2000. David Easton focuses on the study of political system; his model is helpful for understanding the causal relations in my research project. The hypothesis here is that the input of the cooperation between KMT and CCP influences the political environment in Taiwan, thus creates the output, which is the China policy. For the KMT, the negative results of the first two experiences of the cooperation led it adopt the policy of besieging PRC government after its domain moved to Taiwan. This policy had lasted for thirty years. Not until the international environment had changed did KMT adjust its policy. On the other hand, DDP has been standing on the Left side of the spectrum. The subjectivity of Taiwan has always been its main concern. DDP recognizes the PRC government, but rejects the interaction between the two sides in the governmental level. This is mainly because the dramatic discrepancy of their ideology. Furthermore, both KMT and DDP prefer keeping distance with PRC, for they resent the PRC’s policy of unification and cooperation among multiple parties. However, the decision-making process of their China policy is still under the influence of the cooperation of KMT and PRC.