Abstract: In order to increase the capacity of hydrocyclone for oily wastewater cleanup, applying gas flotation theory and utilizing nikunipump to inhale air and water, oily wastewater and air can be mixed evenly under certain pressure, and masses of micro-gas bubbles are produced in the nikunipump. Then the mixture of oily wastewater and micro-gas bubbles are pumped into hydrocyclone to be separated. This (paper) mainly studies the influence of inputting gas on the relations of pressure fall and inlet liquid volume, distributive ratio and pressure fall, oil density and separating efficiency and gas bubbles quantity and separating efficiency. It is discovered that the existing of micro-gas bubbles can enhance the capacity of hydrocyclone obviously(about 20%) under proper conditions and scope limitation of air inhaled(4%~5%).