Abstract: This paper analyzes the liquid physical characteristics affecting hydrocyclone performance, describes both the preparation method of simulated oily water with different dispersion degree and the measuring method of hydrocyclone's grade efficiency, birefly introduces the configuration parameters of hydrocyclones and experimental method, and mainly studies the influence of reject diameters and inlet dimentions on hydrocyclone performance. The series tests have keen carried out so as to improve the performance of hydro-cyclone and decrease energy consumption. The experiment and research results can be applied to the optimal design of liquid-liquid hydrocyclone.