While a state meet the external threat or pressure, it may adopt some means like balancing、bandwagoning or buck passing to response to the situations As for Taiwan, when dealing with threat of China, Taiwan's strategy is balancing and engaging. However, in real world, tension and paradox are disturbing the use of the two strategies. And they also hinder each other hence make them ineffective. This paper discusses with Randall Schweller's underbalancing theory and uses it to research on Taiwan's mainland China policy during 1996-2004. The research shows that President Li Deng-hui belongs to additional model and President Chen Shui-bian belongs to underbalancing through wishful thinking model. Both of their policy outputs approaches Schweller's models.