Based on the numerical simulation of gas flow in an oil-gas separator,traces of different diameter oil droplets in the separator were simulated using the discrete random walk model.The sizes of oil droplets at the outlet of the oil-gas separator were measured by Malvern analyzer. Separation efficiency of the separator was tested with different discharge pressure and mass of oil injection.The results show that the traces of different diameter oil droplets are different,and the corresponding separation efficiency and the separation time are not the same.The larger diameter oil droplets are separated easily.The separation efficiency increases with the increase of the oil injection mass,however,it increases and then decreases with the increasing discharge pressure.When the discharge pressure was 0.65 MPa,the maximum separation efficiency is obtained.The simulation results indicate that under the calculation condition,the minimal diameter of oil droplets separated completely by the separator is 16 μm.And the measured maximal diameter of oil droplets at the separator outlet is from 17.7 μm to 20.5 μm.The simulation results are in agreement with the experimental data.