Abstract: A driver's behavior of controlling a vehicle will be influenced if the sight distance is insufficient. Thus it causes the change of the vehicle's operating speed and the start or termination of the overtaking.Because sight distance changes with the road traffic condition at any time and any place,most simulation software does not consider the effect of sight distance on vehicle's speed and overtaking.This paper propounds a way and automatic calculation procedure for sight distance to different road alignment,offers some help to simulate the real traffic flow characteristic according to the sight distance in the simulation system.