In consideration of the uncertainty of PPP project benefit, firstly a relative index to describe the operating compensation for the project is introduced to design a single period compensation contract based on the government’s need. Then based on the fact that the private investment variable can’t be included in the contract, a game model between the public and private sector is proposed to explore the contact’s optimal form, incentive effect and valid condition respectively from the centralized and disperse decision-making. The research results show that the obtained optimal contract can encourage the private investor to choose the same optimal investment scale as the government’s centralized decision-making, and share both risks and revenues with the government. However, the valid compensation must satisfy the project’s social welfare constraint, which implies the valid compensation should be adapted to different actual scenes for PPP project.