The working environment of LHD is very bad, the functions realization including transport, loading and unloading, walking, braking and steering need hydraulic system all, whose performance and reliability directly affect the vehicle. According to the structure characteristics of ACY2 type underground loadhauldump(LHD) hydraulic system, the improved design to ACY2 type underground LHD hydraulic system was carried on referring to TORO007 type underground LHD. According to classical design experience, the comprehensive resistance coefficient between the tire and ground was reduced from 05 to 016; the steering hydraulic cylinder diameter was reduced to change double pump displacement; brake system was changed from hydraulic brake to brake spring; the analysis models of the hydraulic system that before and after optimization were built based on Automation Studio and the system parameters were adjusted. The improved design and the original design parameters of the hydraulic system were comparatively analyzed, and the steering and braking performances were comparatively analyzed. The results show that: the performance of the braking hydraulic system is more safe and reliable, the pressure in the system is reduced, the local pressure drop is reduced. The improved design system has better effect.The research provides reference for similar design.