The numerical simulation of the internal flow field of a gravity type oil-water separator with different entrance components was carried out to obtain the internal velocity vector and flow field of a separator of three exit positions,four angles of incidence and four different axial positions of the inlet tube,through the standard k-ε model of Fluent software for turbulent flow calculation.The analysis of the comparative study results showed that the smaller the distance from the inlet tube exit to the top inner wall of the cylinder,the better the hindrance of the cylinder to the incident fluid,and the smaller the vortex area after the fluid passed through the rectifier.When the angle of incidence was 30°,60° and 120°,the vortex was generated behind the rectifier,and the flow field was turbulent.There was no vortex at 90°,and the fluid flow was relatively stable.The closer the inlet elbow was to the head,the smaller the vortex area in front of the rectifier and the better the rectification effect,and the more the axial flow ratio of the flow field at the rear flow field,the more favorable separation of oil-water phase.