This paper studied the attitude stabilization of a 3D rigid pendulum with sliding mode control method. The 3D rigid pendulum consists of a rigid body supported by a fixed and frictionless pivot with three rotational degrees, acted on by a constant gravitational force. Considering the attitude control of the 3D rigid pendulum at equilibrium position, this paper has designed a sliding mode controller and analyzed the asymptotic stability of angle velocity and attitude. Then the sufficient conditions of the sliding parameters were gained according to the Lyapunov direct method, and numerical simulation results show the validity of the controller.