For the problem of pavement hardening in underground metal mine,a mine concrete mixer truck was designed.In order to meet the requirements of underground operation and meet the requirements of steering,braking,feeding,drumming,unloading and emergency unloading,four wheel driving and fourwheel steering was used to increase the maneuverability of the vehicle.So the hydraulic system of the truck was more complex.The principle of the hydraulic system various parts,and the selection and calculation of the parameters were mainly introduced.