Abstract: In order to analyze the necessity and feasibility of close-loop process control by electro-hydranlic ration in the friction welding, the static and dynamic characteristics and the axial pressure fluctuations in long period welding production of two hydraulic systems of friction welding machine were compared. One system is constructed with stationary valves and the other used proportional relief valves.The effect of system oil temperature on axial pressure was analyzed in emphases.The results show that the static and dynamic characteristics of axial pressure with the proportional valve system are better than those with the switch valve system;the axial pressure of the proportional valve control system is independent on oil temperature.In long periodwelding production, the control precision of axial pressure with the proportional valve control system is higher, and the repeatability is better than that of switch valve control system.