In order to exploit the advantages of operation and management of social capital in PPP projects better, as well as optimize the income distribution because of the information asymmetry between the government and the social capital, technological innovation and inhibit opportunistic behaviors are studied in detail. Considering behavioral cost and risk cost of two behaviors of the agent, as well as the influence in total income of incentive and penalty, an incentive mechanism model for PPP project is established based on the Principal-Agent Theory. The optimal incentive and punishment coefficient of the government and optimal effort level of two behaviors of the social capital are obtained by calculating the model in first-order approach. Effect of risk perception and two behaviors abilities of social capital on effort level of social capital and income distribution are obtained by analyzing the optimal solution of the mode. The analysis results are verified by assigning parameters in the model and using MATLAB software for numerical simulation. The results show that there is a positive correlation between ability and effort level of a behavior and a negative correlation between the risk perception and effort level.