Aiming at the problems of pressure oil leakage, parameter uptake, hysteresis, and oscillation in electro-hydraulic servo systems, a linear self-immunity control method is proposed, which uses a second-order linear expansion state observer to actively estimate the internal and external perturbations of the system in real time and a proportional-integral control control law with acceleration feed-forward to suppress the internal and external perturbations of the system. Aiming at the problem that the linear self-immunity parameters are difficult to be adjusted, an improved genetic algorithm is proposed to optimise the parameters of the linear self-immunity controller, searching for the best parameter combinations to improve the system control performance and immunity to disturbances. Through simulation and experimental analysis, the disturbance suppression ability of the system is improved by 66.8% under the disturbed state, and the position tracking accuracy is improved by 60.2%, which verifies the stability of the proposed method, and reveals the influence law of linear self-oscillating parameters on the control performance.