This paper discusses the cost and benefit of the cross-river Bridge PPP construction project in Y City, and analyzes the application of PPP model in China and its economic benefits. Research shows that PPP model not only effectively alleviates traffic pressure and promotes regional economic development, but also significantly reduces project construction and transportation costs and improves the quality of public services through social capital investment and operation. As a typical case, the cross-River Bridge project accounts for 95% of social capital, and its successful implementation validates the significant advantages of the PPP model in improving economic and social benefits. In the national economic evaluation, the project made fine adjustments to the investment cost, including the application of shadow price and the adjustment of the conversion factor of labor wages, to ensure the accuracy of the evaluation results. In addition, the technical and economic data of various types of motor vehicles are listed in detail, especially the adjustment of the cost of motor transportation related to time, which provides an important cost reference for the transportation industry. Through the comprehensive analysis of the theoretical basis, practical application and economic cost and benefit of PPP model, this paper not only enriches the cost and benefit analysis theory of PPP projects, but also provides valuable practical experience and theoretical support for similar projects. Looking ahead, suggestions such as improving the governance system and strengthening risk management and control will promote the widespread application of the PPP model in China and inject new vitality into economic and social development.