In order to solve the inadaptability problems of traditional tractors in hilly areas,a new hydraulic driving system for hilly tractor was designed.Based on the actual demands,the technical scheme of the hydraulic driving system was proposed.In the hydraulic driving system,closed circuit of one pump and four motors was adopted and the synchronous motor was used to prevent the wheels from slipping.The parameters of main hydraulic components were calculated,and the designed hydraulic system was modeled and simulated in AMESim software.The simulation results show that the working pressure,output torque and output rotation speed of the hydraulic system are 19.204 MPa、339.01 N·m and 62.14 r/min respectively,which are in accordance with the design parameters,and the feasibility of the system are verified;when the synchronous motor is out of work,the slip of one of the tractor wheels will cause driving capacity loss,the operating pressure is only 1.838 MPa;if the synchronous motor is compelled to divide flow at this time,the operating pressure increases to 19.197 MPa,and then the tractor will regain driving capacity.The research methods provides some references for hydraulic driving system design of other agricultural machinery.