Abstract: Liquid/solid hydrocyclones are widely used in industry and their separation efficiency is an important parameter in evaluating theperformance. In this study, the relationships between separation efficiencyand liquid velocity, oil/water ratio, as well as stage number areinvestigated. The reason why particlesof smaller-diameter more sensitive to thechanges of parameters is explained through a force balance analysis.Moreover, the relationship between separation efficiency andReynolds number, Stokes number is obtained based on dimensional analysis.Finally, some suggestions are made for the application ofliquid/solid hydrocyclones.