Aimed at vaired characteristics of the displacement control system parameters of a large type of fixed hydraulic crusher, the mathematic model of the contol system of boom of the crusher was established. The relationship between its equivalent mass, natural frequency, damping ratio and orientation of boom, secondary arm was analyzed. The controlling effects were researched of traditional proportion integration and differential (PID) control and the sliding mode variable structure control algorithm based on exponential approaching rate. Simulation results show that the sliding mode variable control algorithm based on exponential approaching rate responses quickly and is of strong robustness capacity, and much better than the traditional PID control in performance.