Flash welding is the most important welding method of jointless track in field rail. Because its heating is mainly achieved through the resistance heat of a short circuited liquid bridge. As a result,the liquid bridge existing time affects the heating and end surface’s state. However,the existence time of the liquid bridge is affected by the dynamic performance of the movable clamp of the welding machine. Therefore,aiming at the specific field construction conditions of rail flash butt welding,based on the actual system,under the environment of MATLAB,using Sim Hydraulics software to establish the hydraulic simulation model of forging system of flash welding machine. And the dynamic response of the movable clamp is simulated and analyzed in the case of different structural parameters of the oil system and the change of the load. The results show that the dynamic response speed of the movable clamp can be effectively improved by reducing the diameter and length of the tubing and increasing the hydraulic system pressure of the handpiece. When the welding environment changes,the dynamic response of the movable clamp can be guaranteed by changing the setting value of the hydraulic system and adjusting the control algorithm,which provides the direction for the quality assurance of the welding field.