In order to study the influence of vehicle entering and leaving at the exit of the parking lot on the speed of vehicles on the connecting road, this paper analyzes the influencing factors such as the size of the park- ing lot, the exit rate and the length of the entrance road. It used the time obstacle rate to reflect the impact of the parking vehicle on road traffic. By taking the parking effect as the traffic impedance of the vehicles in the section, it established the main road vehicle speed model for different types of vehicles based on the model of BPR. Then, it simulated a parking lot and connecting road using the VISSIM simulation software. Comparing the result calculated by the speed model and the simulation result, it found that the speed model can accurately de- scribe the impact of parking lot on the vehicle speed of connecting road.