In order to ensure that upstream vehicles can successfully pass accident influence area, and avoid traffic congestion and secondary accidents, mandatory lane-changing model based optimization was built. Optimization selection model of feasible point and lane-changing mode was set up, and the optimization goal was to minimize the sum of longitudinal travel distances of lane-changing vehicles and the constraint were the minimum safe space and time of lane-changing completion. To verify the effectiveness of the proposed method, a case study was carried out, and calculation results of different initial flow and speed were analyzed. Calculations prove that initial flow rate and speed have an important influence on the lane-changing mode and the lane-changing point. The model proposed can effectively optimize the vehicle’s changeover point and the lane-changing mode.