Considering the high-density characteristics of urban road traffic, the impact of lane-changing process is distinguished from the acceleration change caused by traffic density after lane-changing. A traffic flow dynamics equation considering the impact of lane-changing process is proposed. This method first converts the reduction coefficient of the Laval model with the nature of lane-changing competition and balance into the difficulty of lane-changing, and then through the comparison of the difference calculation, the calculation method of the lane-changing influence item is given when the traffic flow is not smooth. The results show that the dynamic equation can describe the traffic flow behavior under high-density conditions, and express the viscosity of the traffic flow caused by the target lane and the departure lane.