Liquid/solid hydrocyclones are widely used for various applications. Based on massive experiments, the relationships between separation efficiency and liquid velocity, oil/water ratio, as well as the number of hydrocyclones were investigated. The phenomenon of smaller particles more sensitive to changes of parameters was explained theoretically through force balance analysis. Besides, the dependence of separation efficiency on the Reynolds number and the Stokes number was regressed based on dimensional analysis. Finally, some valuable suggestions were put forward for the practical application of liquid/solid hydrocyclones.