To improve the oil-water separation efficiency, a U-tube separation structure is proposed since the seperation efficiency of the existing T-tube separation technology is relatively low. In order to verify the performance of the new tubular separation structure, the variation of the internal flow field of the U-tube oil-water separation device is studied by Fluent quantitative analysis. The research mainly focuses on the influence of some external parameters such as inlet velocity, inlet oil content, rotation radius, oil droplet size and α angle on the separation efficiency of the U-tube. The main conclusions are as follows: the inlet velocity of the mixture has a great influence on the separation efficiency. The oil-water separation rate decreases with the increase of the inlet velocity, the oil-water separation rate increases with the increase of the rotation radius of the U-tube, but when the radius of rotation exceeds 0.6 m, the separation efficiency no longer increases significantly, and the oil-water separation rate gradually increases as the oil droplet size increases. The research results provide a reference for the design of oil-water separation U-tube.