In this paper, a novel dynamic de-oiling oil-water separator was proposed. The effects of the split ratio and the pressure drop ratio on the separation efficiency were investigated through theoretical analysis and Computational Fluid Dynamics (CFD) simulation. Pressure ratio variations were achieved in two ways. First, a certain pressure was maintained at the oil outlet and the inlet pressure was allowed to increase steadily, which resulted in the pressure drop ratio initially decreasing till reaching the convergence value. Second, while maintaining a given inlet pressure, there was a linear relationship between the decrease of the pressure drop ratio and the increase of the pressure at the oil outlet. However, in both circumstances, it was clear that the separation efficiency initially increased and then kept steady as the pressure drop ratio increased, during which the split ratio decreased approximately linearly. In addition, optimal combination properties could be obtained when the pressure drop ratio was set at a specified value. The separation efficiency and the split ratio both perform good results.