In comprehensive passenger transportation terminal, the passenger congestion is one of major problems and thus many ways have been taken to mitigate it. It is believed that an appropriate selection of congestion mitigation strategies comes from the sound understanding of the congestion characteristics. In this paper we analyzed the main reasons, simulated the process of its formation and aggravating by AnyLogic. Then we obtained the data about the varying passenger flow density changing along with time and place. Based on the simulation data, we research the characteristics of the congestion occurred in the transportation terminal from the perspective of the passenger flow density, which offers some references to mitigate the congestion.