The reaching law is a convenient method for the design of sliding mode control. This method retains the robustness of the sliding mode control and makes the reaching speed adjustable. In the design of the sliding mode control for system with steady-state error which caused by disturbance, the traditional reaching law cannot eliminate the steady state error, in other words the states of system cannot be directed to the sliding surface. To solve this problem, the integral method is introduced in the reaching condition to develop two new reaching conditions. The new reaching conditions can eliminate the steady state error caused by modeling error and nonlinear disturbance, and direct the states of system to the sliding surface accurately. Electro-hydrostatic actuator (EHA) is the key component of the power-by-wire actuation system (PBW). The actuation performance directly impacts performance of the flight control system. The actuator is a nonlinear system with steady state error. Using these two reaching laws to design the sliding mode control of the actuator. Simulation results show that the sliding mode control based on the new reaching law eliminated the steady state error and improved the control precision.