Hydraulic dampers are widely used in various bridges,railway continuous beams,and seismic retrofits of bridges in China due to their excellent characteristics.In order to study the internal influence mechanism of frequency dependence of dynamic stiffness and amplitude of hydraulic damper,a mathematical model of damper force considering the compressibility of damping medium was built,and a simulation model of hydraulic damper was built using AEMSim software.The hydraulic damper was tested on site,and the simulation results were compared with the test results.The results indicate that the dynamic stiffness of the hydraulic damper increases with the increase of loading frequency; the amplitude decreases with the increase of loading frequency; the compression characteristics of damping media are key factors affecting the dynamic stiffness and amplitude of dampers.