Modified rodrigues parameters(MRP) sliding mode control law was designed considering actuator character. Spacecraft attitude dynamics with double-gimbaled control moment gyro (DGCMG) and kinematics on MRP were founded. The model uncertainties was analyzed so that whether sliding mode control can be used here is known. Then sliding manifold was chosen and the corresponding control law was presented while estimating the parameters of the controller on the base of linear system theory and Lyapunov theory. The Monte Carlo simulation proves that this controller can execute attitude control well, precisely and robustly.