Private equity makes investment decision to build trust-based relationship with enterprises which aims at sharing resources and achieving common goals. It is not only the relationship between legal people, but also the human to human relationship between the investor and entrepreneurs. Due to the asymmetry of information and uncertainty of the future development, the formal agreements cannot be perfect and trust is the key to the belief that no one will use this uncertainty and the premise of cooperation. The study of relationship between PE and enterprises in western countries mostly focuses on principal-agent theory, taking the formal control mechanism as the governance form of relationship. However, the ranking of emotion, morality and law inChinais different from that in western countries. If we emphasize control too much, it will weaken mutual trust and make bad influence on investment cooperation. PE leads the enterprise to realize the value of cooperation in the future and the society network of PE, emphasizing the society reputation, forming the common value and establishing informal control. All these are the important variables in deciding trust and cooperation.