<p>Improving the automatic leveling efficiency of a load platform is critical to the running safety of an Automated Guided Vehicle (AGV). In this paper, an adaptive sliding mode controller (ASMC) suitable for large disturbances is designed for automatic leveling of the load platform of a heavy-duty AGV equipped with four hydraulic actuators as active suspension systems. A full-vehicle suspension model with uncertain parameters and external disturbances is established. Sliding mode equivalent control terms are derived for the heave, pitch and roll subsystems. The sliding mode switching control term is optimized based on a continuous function to ensure that the controller can effectively adjust the AGV vehicle attitude. The adaptive law is derived to enable the controller to adapt to the uncertainty of the vehicle body parameters. The efficacy of the ASMC is evaluated through the implementation of simulation studies. The simulation results of the specific examples show that the control strategy can significantly enhance vehicle stability in the presence of complex road conditions while simultaneously guaranteeing the running safety of AGV. In comparison with passive suspension (PS) and adaptive backstepping controller (ABC), the control strategy presented in this paper demonstrates great superiority in enhancing the horizontal stability of the AGV body during transportation.</p>