Abstract: To find the motion law and optimum size of floatation bubbles in a three-phase flow,the Eulerian model is used to simulate the motion process of bubbles with different initial diameters in pulps of different concentrations. The simulation results show that under the given initial condition,in the pulp with a certain concentration,bubbles of 4 mm catch the most mine grains; bubbles of any size above or below 4 mm cannot capture mine grains as many as those of 4 mm. When the pulp concentration is in the range of 20%-40%,the size of bubbles that capture the most mine grains does not change much. As the pulp concentration increases,the amount captured by a single bubble increases,so does the recovery rate of mine grains. In real production,bubbles of 3.5-4 mm have small deformation,moderate horizontal shift and lifting speed,and strong ability of capturing and carrying mine grains and lifting,which are benefit for improving the quality and quantity of floatation production.