Abstract: This paper attempts to reduce the social cost caused by traffic pollution in urban traffic network through reasonable urban traffic planning. A network optimization model based on the social cost control of traffic pollution is established，and an example is given to compare the results of the equilibrium assignment model，the shortest path equilibrium model and the exhaust pollution network optimization model. It provides different research perspectives for urban traffic assignment.

Key words: traffic assignment, motor vehicle exhaust pollution, social cost, network optimization model