The main factor influencing the efficiency of oil-water separation is the coalescing internals. Based on practical experience, the separation effect of oil-water phase is improved, and the internals occupy a small space within the effective separation section of the equipment. Different types of plate have different effects. If physical tests are to be carried out one by one, the research costs would be too high and the duration is too long, which cannot meet the production needs. In recent years, computational fluid dynamics has become an important tool in engineering design and is a scientific research method in many engineering fields. Therefore, in this paper, through numerical simulation calculation of different structural forms of oil-water separation coalescing internals, and analysis and comparison of the calculation results, the optimal structural parameters are obtained and applied to the new oil-water separation equipment. Field comparison test shows that the efficiency of the new oil-water separation equipment is multiplied by 3.7~3.8. This research can provide significant reference and guidance for the research on improvement of oil-water separation efficiency.