To study the impact of traffic incidents on urban expressway,the forecasting model of traffic incident influence is established on MCTM model. With regard to the metastable phenomenon of urban expressway traffic flow,the traffic flow state of metastable region is simulated in this model. Besides,the impact of traffic incidents on the main traffic flow features of the cells is considered and the setting of the cells is adjusted with the location of traffic incidents. And the length of the incident is selected as an evaluation indicator of traffic incident influence. Finally,based on the traffic incident data of Beijing partial road network,the model parameters are calibrated and the influence of one traffic incident is analyzed. The results show that the trends of the simulation data are basically the same with the measured data and the error is within an acceptable range. This model can clearly reflect the state of the traffic flow at different times of the individual sections,and it can determine the traffic incident influence of urban expressway effectively.