Abstract: Micro-emulsion Collector (MEC) has better dispersion performance in coal slime than diesel and emulsified diesel,which can effectively reduce the amount of coal flotation agent. The stability of MEC is an important perform-ance index affecting its industrial application. Domestic and foreign scholars usually use static observation method to study the stability of emulsified diesel and micro-emulsified diesel,which is difficult to visually and quantitatively char-acterize the stability and droplet size of micro-emulsion. In this paper,the effects of emulsifier formulation and dosage, ultrasonic power and duration of action on MEC stability and droplet size were studied by means of Multiple Light Scattering Stability Analyzer. The flotation performance of MEC was investigated by coal slime flotation test. The results showed that the optimum process conditions for the preparation of MEC were:the consumption amount of emulsifier was 5% of diesel,the water content was 5% of diesel,the formulation of the surfactant was Span80 ∶ Tween40 ∶ Octa-nol = 7 ∶ 3 ∶ 4 and the duration of 200 W ultrasonic action was 5 minutes after stirring for 10 minutes. The emulsifier formulation and amount affected the stability of the MEC and the droplet size. The more the emulsifier was used,the more stable the MEC was. When the amount of the emulsifier was 3% ,the droplets were likely to aggregate,and the droplet size would exceed 100 nm after being left for a while. When the amount of emulsifier was 7% ,the MEC was the most stable,and the initial droplet size is 69 nm,which gradually increased with the increase of the standing time. When the amount of emulsifier was 5% ,the stability of MEC was good,and the droplet size did not change with the increase of the standing time,which remained at about 37 nm. When the ultrasonic power was lower than 600 W,the smaller the power,the more stable the MEC was. When the power was greater than 600 W,the greater the power,the smaller the droplet size was,and the better the MEC stability was. When the ultrasonic treatment time was 20 minutes,the Turbiscan Stability Index (TSI) of MEC increased rapidly with the increase of standing time,and MEC was very unstable. When MEC is used for flotation of coal slime,it can significantly increase the contact angle of coal samples,increase the hydro-phobicity of coal particles,and improve the floatability of coal particles. With the same amount of collector,the yield of flotation clean coal is higher,the ash content is lower,and the flotation improvement index is better.