The cooperation between government and social capital，the Public-Private Partnership model，is an important model for providing public goods. Public-Private Partnership is not only a means of financing，but also a contract-based benefit sharing and risk sharing mechanism. Based on the Incomplete Contract Theory，this paper believes that the allocation of control rights is the key to affect the efficiency of Public-Private Partnership. Under the assumption that the proportion of project income distribution is specified in the initial contract，the investment of both parties can be subdivided into public welfare investment and self-interested investment. Through model analysis，the paper studies the incentive effect of control rights on both inputs under different parameter conditions.