In order to study the mechanism of the elastohydrodynamic lubrication of the slipper, the dynamic characteristics of the oil film of the piston pump slipper were numerically simulated. A discretization model of the slippery oil film was established, the oil film pressure distribution was obtained by solving the Reynolds equation of the skid oil film; the coupling relationship between the oil film thickness of the slipper, the pressure distribution of the oil film and the dynamics of the slipper was considered, the oil film thickness change rate was obtained by solving the slipper dynamics equations, and the dynamic pressure distribution and oil film thickness of the slippery sub-oil film were updated. MATLAB software was used for simulation to analyze the dynamic pressure distribution and thickness variation rule of oil film of the slipper and reveal the dynamic characteristics of oil film of the slipper. The research results provide reference for improving the oil film bearing capacity of slipper and reducing power consumption of the piston pump.