A cellular automaton model for two-lane traffic with vehicle mixing basing on the Nagel-Schreckenberg (NaSch) model is proposed. With different parameters, we simulated the traffic flow of the two-lane system when the vehicle densities of lanes are equal or different respectively. The fundamental diagrams of the traffic flow are given. According to the analysis, the traffic state could be divided into three regions.The nonsymmetry of car density on two lanes has important influence on the traffic flow.