Aiming at the heterogeneity of operation costs around private enterprises in PPP projects, this study designs the incentive mechanism to restrain private enterprises from misreporting cost information. This study establishes a principal-agent model. Through designing of the optimal contract that takes price compensation as the incentive measure, the gain of private enterprises by claiming false cost information is not greater than that of reporting his true cost information, which can encourage private enterprises to show their true cost information. Then, we further analyze the influence of enterprise type distribution on the optimal incentive contract. Results show that the incentive mechanism can screen the cost information of private enterprises. In addition, the charge price of private enterprises and the price compensation of government departments are related to the distribution of enterprise types. And the promotion of competition among enterprises will inhibit private enterprises from seizing information rent.