Abstract: For enhancing the flotation of lignite,a new flotation method for the introduction of ultrasonic wave in flota- tion pulp was proposed. The results show that the yield of ultrasonic flotation clean coal is 20. 31% higher than that of the conventional flotation clean coal,the ash content is reduced by about 7. 94% ,and the yield of -0. 045 mm is in- creased by nearly 2 times. Using screening,scanning electron microscopy,X-ray photoelectron spectroscopy,induction time measuring instrument to study the influence of ultrasonic treatment on slime particle size and surface properties, the mechanism of ultrasonic enhanced lignite flotation was investigated. The effect of ultrasonic cleaning and breaking on the surface of coal particles decreases the adhesion of fine particles on the surface of the particles,but does not change the surface hydrophobic and hydrophilic functional groups. Ultrasonic waves can produce a large number of mi- crobubbles in the flotation pulp,which can be adsorbed on the lignite surface to enhance its hydrophobicity and in- crease the collisions / adhesion efficiency of coal particles and bubbles. To a certain extent the cavitation of the ultra- sonic waves causes the hydration film on the surface of the coal to become thinner-unstable-easy to rupture,further en- hancing the flotation recovery of lignite.