The invention provides a walking driving system used for a hydraulic four-wheel drive agricultural machine. The walking driving system comprises a hydraulic mechanism, a driving wheel driving mechanism and a steering wheel driving mechanism. The hydraulic mechanism comprises an oil tank, a closed variable plunger pump, a closed quantitative plunger motor, a free wheel valve group and two low-speed large-torque motors, and the oil tank, the closed variable plunger pump, the closed quantitative plunger motor, the free wheel valve group and the two low-speed large-torque motors are connected through hydraulic pipelines in a matched mode. The closed variable plunger pump drives the closed quantitative plunger motor. The closed quantitative plunger motor drives two walking driving wheels thorough the driving wheel driving mechanism. The closed variable plunger pump drives the two low-speed large-torque motors through the free wheel valve group. The two low-speed large-torque motors drive two steering wheels through the steering wheel driving mechanism. Hydraulic four-wheel drive is achieved. Meanwhile, operating personnel can adopt four-wheel drive when the load is large and adopt two-wheel drive when the load is small, switching is easy, and energy is saved.