Based on the theory of system dynamics, the paper analyzes the mechanism of socio economic benefits of highway projects and establishes the system dynamic model of regional economic－public road transportation. Then taking Jinji highway project of Tianjin as an example, the error of system simulation tested and the system dynamic model built are verified to be quite stable, which have a high performance. Through the comparison of simulation results of Jinji highway being built or not, the paper simulates and predicts the socio economic benefit of each year from 2003 to 2013. Thus the quantification evaluation of socio economic benefit of highway project is realized and it will provide the theory instructions for similar projects in the future.