In order to discuss the characteristics of urban expressway traffic flow, traffic flow simulation was performed for four modules of the expressway. Based on the classical Cell Transmission Model (CTM), according to the basic principle of equal flow transmission between neighboring cells, cell length parameters were introduced and the formula for intercellular communications was deduced. An improved cellular transmission model was proposed. The use of the improved cell transmission model for urban expressway traffic flow simulation mainly includes two aspects of road environment and traffic environment, namely, the distance between the upper roads and the ratio of the main line and the tunnel flow. And the simulation includes four modules that constitute the urban expressway: Basic road section, Confluence area, Triage area, and Weaving area, and use vehicle delay as an analysis indicator. The simulation results show that the increase of delays in the Basic road section and the Triage area is the same, and the increase in the delay in the Converging area and the Weaving area is the same.