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• A disturbance coupled nonlinear model of electro-hydraulic load simulator containing the mechanical backlash influence is proposed to increase the system modeling accuracy. • The mechanical oscillation phenomenon in the system is analyzed under different disturbance situations and parameter variation conditions to explain the necessity of adopting an oscillation reduction algorithm. • An almost disturbance decoupling control strategy is proposed to reject the external position disturbance and mitigate the oscillation caused by the discontinuous mechanical backlash. • The boundary and the convergence speed of the force tracking error are derived to guarantee the system performance, which are verified by both the simulation and experimental results. This paper proposes an almost disturbance decoupling (ADD) control strategy for solving the force control problem of an electro-hydraulic load simulator containing mechanical backlash. This method can enhance the force tracking performance of the load simulator by decoupling position disturbance and mitigating the backlash effect. Based on a proposed disturbance coupled model of the load simulator, the necessity of adopting the ADD control is explained by the mechanical oscillation analysis with a simple controller under different disturbance situations. Then, the design method and tuning parameters of the ADD controller are discussed. With the ADD controller, the system's input-to-state stability with respect to disturbance signals is guaranteed, and moreover, the boundary and the convergence speed of the force tracking error are adjustable by tuning the controller parameters. Both simulation results and experimental results demonstrate that the proposed ADD control can achieve much higher force tracking performance than a controller commonly used in industry. [ABSTRACT FROM AUTHOR]