When the three axis machine tool moves along the linear trajectory, its speed, acceleration and jerk are not continuous at transition points. It directly affects the movement state of cutting tool, so as to reduce the precision of surface. An optimization method was proposed, through the insertion of cubic Bspline at the adjacent position of the tip point, a continuous optimal tool position spline curve could be gotten which had threeorder continuity at the connection point. By this method, the cutting tool can be smoothed in the corner, while the speed and acceleration are continuous, and the cutter trace can be avoided. Finally, the experimental results prove that this method can improve the processing quality of the product compared with the traditional linear interpolation.