Abstract: As a collector for coal slime flotation, diesel oil has poor dispersion and collection effect and large dosage. In order to improve the dispersion and collection performance of diesel oil. Two surfactants, Span80 and Tween80, are used to emulsify diesel collector for coal slime flotation. A new collector ST-diesel microemulsion with droplet size less than 100 nm is being prepared. The improvement effect of slime flotation index is studied by unit flotation test. The mechanism of microemulsion on the surface of coal slime is discussed by means of contact angle test, Zeta potential analysis, infrared spectrum analysis and EDLVO theoretical calculation. When ST-diesel microemulsion is used as coal slime collector, the flotation effect is better, and the recovery rate of combustible body can reach 68.13% which is 9.23 percent higher than diesel collector. The contact angle of pure coal surface increased by 17.3° after ST-diesel microemulsion treatment compared with diesel. The absolute value of surface Zeta potential decreases. The energy barrier of the total energy V_T of the interaction between coal particles is reduced, which is beneficial to the agglomeration between particles. The physical adsorption of surfactant and oxygen-containing functional groups on the surface of coal slime improves the surface hydrophobicity of coal particles. The ST-diesel microemulsion can be used as a new and efficient collector for coal slime flotation.