The half suspension model established in this paper fully considers the non-linear characteristics of single-rod hydraulic actuators, and designs a sliding mode adaptive controller based on the existence of uncertain parameters and possible external uncertain disturbances in the system. Considering that some of the state variables required by the controller are not easy to obtain, an extended state observer is designed to observe the wheel vertical movement speed and the pressure of the rod cavity and non-rod pressure of the hydraulic actuator.