In order to study the motion characteristics of a high-speed switching valve used in the pilot stage of proportional directional valve,a UDF program was written to control the valve core movement under the joint action of fluid force,spring force and electromagnetic force.The fluid-structure coupling simulation of the valve was realized by dynamic mesh,the precise movement of the valve core and the change of the transient flow field were obtained.The results that the written UDF program can accurately simulate the valve core movement state during actual work,and the valve opening time is 1.8 ms.This research method can obtain the precise motion characteristics of high speed on-off valves and provide guidance for the optimization of high speed on-off valve products.