Abstract: In order to investigate the law of the emulsion breaking of the flotation reagent emulsified by jet emulsifier,thus provide basis for mounting position of jet emulsifier in coal washing system.Metallographic microscope and color computer image analysis system were used to analyze the time expend of emulsion breaking of the emulsified diesel made by jet.The results shows that-20μm emulsified droplets share 97% in all,the average breaking time for diesel’s emulsion is 42.3s,so that the mounting position of jet emulsifier should in the range of 42 meters between dosing point and the flotation machine.