The automatic aiming system of rocket launcher is divided into two subsystems, one is elevation sub-system, and the other is azimuth sub-system. There is coupling nonlinear torque between two subsystems when acting together, which can influence the accuracy of the control, even causes system divergence. In view of these characteristics, the system was made input-output decoupling linearization approximate. On this basis, a dynamic sliding mode control approach was presented to design position controller for precise aiming. Finally, simulation was performed for the comparison study of the classic sliding control and the dynamic sliding control. The results show that the proposed approach is superior to the traditional sliding mode, can realize accurately, rapidly and smoothly automatic tracking .