Abstract: The multi-modal traffic assignment problem with constraints of low carbon emission was discussed in this paper. Taking the energy use per person and pollutant emission into consideration, the user equilibrium model with low carbon emission constraints was presented with combining the traffic modal split and traffic assignment. A real-value encoding genetic algorithm for solving the model was proposed and validated a small network example. Comparison results show that the restriction of private car can achieve the targets both meeting the traffic demand and reducing the carbon emission, which provide the practical policy for the low carbon travel avocation.