Abstract: During the path planning of the robot trajectory track based on vision,it's necessary to reproduce the discrete sampled data into the original curve.The paper provides a new approach of fitting the are and straight lines using the relationship of the arc length and the angle between the tangent of the curve on the point and the horizon. The common two dimension curve fitting methods can't converge the high order derivatives and conquer the data noises. Our method can realize the exact reproduction of the curve.Experiment has been made on our Direct Drive robot.The result is quite good.