The paper proposes an adaptive gain back-stepping sliding mode control (AGBSMC) for tracking position of the electro-hydraulic servo system (EHSs). In the EHSs, there always exist uncertainties and nonlinearities such as friction, leakages, oil temperature which are challenges for the control design. The proposed control includes two sliding mode control. One controls the tracking position in the mechanical dynamic and other drives the pressures in hydraulic dynamic. Additionally, a fast speed adaptive law is investigated to estimate the variant perturbation, and it remains the stability and robustness of the controlled system and reduces chattering effect with the variant uncertainties. Specially the robustness, stability and the adaptive law will be demonstrated and derived by the Lyapunov approaches. Finally, some simulations are set up to demonstrate the effectiveness of the proposed controller, and the proposed controller is also compared with the Proportional - integral - derivative (PID) controller.