Because linear quadratic regulator (LQR) possesses the comprehensive control properties with respect to high precision regulation and small control consumption, it was introduced into the design of crane digital control system, in order to realize the single pendulum of crane quickly return to balance position. The continuous spacestate equation and the corresponding discrete one of the crane system were established respectively. According to the discrete statespace model of the crane system, the control strategy of servo DC motor was designed by using LQR optimal control theory. Computer simulation results present that compared to conventional poles replacement method, the LQR method can realize more faster and more accurater regulation to the single pendulum of crane, and the proposed method can also avoid the complicated process of parameter regulations, therefore it is easy to be implemented in engineering. 