Aimed at the problem of oil leakage in vehicle shock absorber,the tiny oil leakage of the shock absorber was studied by simulation and experiment.The theoretical force analysis of the micro internal leakage between the piston and the cylinder was carried out by mathematical model.The Autodesk Inventor software was used to establish the internal annular gap fluid geometry model of the damper,and the CFD simulation technology was used to simulate the threedimensional model of the annular gap fluid.Through the changes of flow field velocity,pressure,turbulent flow energy and temperature parameters,the main influencing factors affecting the tiny internal leakage of the damper oil were analyzed.The oil leakage test at different piston speed and annular clearance was performed on a servo dynamometer.The test results show that when the piston is stationary,the change of throttle velocity, pressure and turbulent flow energy has a great influence on the oil leakage of the annular gap,and the influence of temperature change is small.When the piston moves,the leakage of the annular gap is increased with the increasing of the piston speed and the gap between the piston and the cylinder.Therefore, the leakage can be reduced by reducing the gap between the piston and the cylinder under the condition that the machining accuracy is allowed.