Abstract: The inclined oil-water separator is a new efficient oil-water separation equipment and the structure of which is designed preliminarily. In order to improve the oil-water separating efficiency, orthogonal design is introduced to optimize the structural parameters. An orthogonal scheme with 8 factors and 5 levels is designed to get 50 different structure models. Fluent 12.0 software was used to simulate the 50 models and 25 schemes of them were selected for visual analysis, as a result, the scheme A was determined as an optimal scheme. By the range analysis of numerical data and the influence analysis of structure parameters on the impact of oil-water separation efficiency, the highest levels of the average oil-water separation efficiency were combined to get an optimal plan B. After comparing A with B, it showed clearly that optimal parameters of the inclined oil-water separator was plan B. By simulating flow field with the same method, it was found that the optimized separation efficiency increased by 4.972%, which showed that orthogonal design in optimizing structure parameters of the separators had some practical significance.