This paper presents a technique for the position servo system of numerical control (NC) machine tool by utilizing the optimal quadratic controller. The mathematical model of the position servo control system is structured, which of the plant model is identified by making use of recursive least square method. The fundamental method of designing the optimal quadratic controller is proposed. Simulation of the optimal quadratic controller and PID controller are implemented by using MATLAB. The results of simulation show that the proposed control method of positional servo control system has better dynamic characteristics and better steady performance.