Based on the introduction of control principle about machining contour of Numerical Control (NC) machine tool, the machining contouring error was investigated with simulation, and a conclusion was gotten that the contouring error was related to the contouring curvature in planned machining and the feed speed of machine tool. In the case that the geometric contouring curvature of workpiece waiting for machining set already, a variable feed speed strategy to optimize the dynamic contouring error of NC machine tool was proposed. The simulation result shows that this control strategy can reduce the amount of contouring error, and promote the machining accuracy of the contour effectively.