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Because of the diversification of resident trip demand and the requirements of urban sustainable development, a new model for traffic mode sustainability assessing was made. The impact indexes of traffic mode on urban sustainable development, e. g. the growth of city’ s GDP, the development of real estate and the service industry, etc. , was determined. In the paper the mathematic methods was applied to evaluate the impact extent of traffic mode on urban development. Two types of impact assessment results were obtained. It helped to accurately orientate the traffic modes. Then, with the evaluation results, the mathematical programming model of transport system mode optimization was made, too. Its abjective was to obtain maximum efficiency of the urban sustainable development. The urban passenger trip demand, capacity of the road system and environmental factors erc were regarded as its constraints. Finally, the model was applied to address the rational passenger transport system mode in Suzhou.