In this paper we present a kind of auxiliary line access method based on image approach to help humanoid robots driving a car in a complicated unknown environments. According to road image taken during driving robot , a point was picked as the next point of the robot driving. According to the location of this point, calculate turning radius. On the steering wheel angle and the turning radius curve fitting, steering wheel angle calculated; According to the Angle of information and draw the vehicle auxiliary line on the image. This algorithm simulated on matlab environment, experimental results show that this method can obtain more accurate auxiliary lines as a reference when the vehicle driving, and bring great convenience to assist the robot successfully driving the vehicle.