The walking system of wheeled vehicle is very important to the reliability of vehicle operation,and its preliminary design determines the success or failure of the project.The U-shaped frame support vehicle with complex principle was taken as an example, the principle of walking hydraulic system was analyzed,and parameters such as walking speed,traction force and engine power were calculated.It provides a theoretical basis for the design of closed walking hydraulic system of engineering vehicles,and the waste caused by unreasonable design is reduced.The model has been tested by customers and all indicators meet the expected requirements.