To realize the trajectory control of excavators arm, the position control of each joint’s cylinder is necessary. The nonlinear model of excavator’s electrohydraulic system was designed. Impedance control was applied because the excavator would move in both free space and constrained space. Considering the nonlinear and uncertainty of excavator’s electrohydraulic system, the sliding mode control with variable switching coefficient was used into impedance control to guarantee high control precision in the presence of uncertainty. The sliding mode control asymptotically drived the system state to implement the target impedance and it could satisfy position control and force control at the same time. Simulation was carried out aiming at the designed controller and the effects of position tracking and force tracking were presented.