Abstract:  The problem of determining the publicprivate investment ratio of publicprivate partnership (PPP) highway and the concession term of private investor is discussed in this paper. By comparing PPP highway project traffic saturation stage with the concession term, two models of decisionmaking on the investment ratio of government and private investors and the concession term are built. With the models, the optimal investment ratio and concession term are obtained, and the maximal social benefit of government departments and benefit of private investor are achieved. At last, an example is used to validate the effectiveness of the decisionmaking model.