In order to implement the independent maintenance requirements of China Railway Group,a study was conducted on the influence of preload on test results during EMU shock absorber maintenance.A certain type of anti-hunting oil pressure shock absorber was taken as the research object,and 3D and flow mechanics models were constructed for the piston damping valve of the shock absorber.Co-simulation software ANSYS and MATLAB/Simulink were utilized to modify preload parameters in order to obtain fluid mechanics changes in the damping valve and damping characteristic curves of the shock absorber.The simulation results were validated using a damper bench,and an analysis was performed on how piston damper valve preload affects damper damping.The test results indicate that when speed does not reach the opening condition of the valve port,changes in damping valve preload do not affect the damping force value of the shock absorber;only when speed reaches this opening condition does preload modification impact damping characteristics;tensile and compressive damping forces increase with an increase in damping valve preload.