Abstract: Under the circumstance of heavy traffic and exhaust gas pollution, the development of public transportation is one of the effective ways to bring down the number of vehicle per capital, relieve the traffic congestion, and reduce the automobile engine emission. On the basis of defining the system boundary and inducing the main influencing factors of passenger flow, the association of these factors is analyzed using Interpretive Structural Model in this paper. Then the relations and structures of these factors are established, and the influence to passenger flow of these factors is interpreted. And then the direct and fundamental method to increase the passenger flow and the utilization of public traffic is suggested.