Abstract: The high degree of oxidation and poor hydrophobicity of fly ash particles result in the formation of stable hydration films that impede the effective adsorption of conventional hydrocarbon-based collectors onto the particle surfaces. Conventional hydrocarbon oil collector can slightly improve the surface hydrophobicity of coal fly ash due to its low adsorption on the surface of coal fly ash particles, resulting in large consumption of flotation agent and difficulty in decarbonization of coal fly ash, thus seriously restricts the recovery and utilization of coal fly ash. In order to solve the problems of poor selectivity, low separation efficiency and serious environmental pollution of traditional collectors in the flotation decarbonization of coal fly ash, biodiesel was selected as the collector for the flotation decarbonization test of coal fly ash. The mechanism of enhanced decarbonization of coal fly ash by biodiesel collector was further analyzed by means of coating angle, saturated adsorption capacity, particle agglomeration behavior, infrared spectrum, gas chromatography-mass spectrometry and other test methods. The test results show that compared with conventional hydrocarbon oil collectors, biodiesel has better selectivity and can improve the flotation effect. When the blend ratio of 1600 and 1030 is 3∶1 and the dosage is 200 g/t, the flotation effect is the best, and the effect of single 1600 and 1030 collectors is comparable. After treatment with different collectors, the coating angle is diesel<1600<1030<composite agent, and the adsorption capacity of deionized water is diesel>1030>1600>composite agent. The particle aggregation size of 0.045～0.010 mm is composite agent>diesel>original sample. Mechanism analysis shows that the polar end groups of esters, carboxylic acids and alcohols in the biodiesel collector form hydrogen bonds with the oxygen-containing functional groups on the surface of coal fly ash to adsorb on the surface of coal fly ash, exposing the hydrophobic end of coal fly ash to slurry, improving the surface hydrophobicity of coal fly ash, making its fine particles easier to agglomerate, thus improving the floatability of coal fly ash and reducing the ash content of foam products. It provides strategies and guidance for the development of green and efficient flotation and decarbonization collectors suitable for coal fly ash.