The efficient and sustainable utilization of resources can be achieved by flotation recovery of high-quality carbon components in high-ash fine-grained coal slime. Taking high-ash fine-grained coal slime as the research object, by compounding octylphenol polyoxyethylene ether (OP-10) and polyethylene oxide (PEO) for pretreatment and comparing with single reagent pretreatment flotation, it was found that the two reagents greatly improved the floatability of coal slime through synergistic effect. On this basis, the mesoscopic mechanism was analyzed by laser particle size analyzer, contact angle measuring instrument, infrared spectrometer (FTIR), Zeta potentiometer and atomic force microscope (AFM). The results are as follows. Firstly, due to the competitive adsorption relationship between the two agents, PEO agents preferentially adsorbed and exposed the alkyl chain through polar forces on the surface of the coal sample to enhance partial hydrophobicity, while compressing the hydration layer on the surface of the slime and reducing the electrostatic repulsion between the interfaces, prompting the fine coal slime to begin to flocculate into small flocs. Secondly, after the completion of PEO reagent action, OP-10 reagent began to adsorb on the surface of flocs, compressing the electric double layer of coal slime and shielding the electronegative ions. Thirdly, the two ends of the structure of the agent were adsorbed by the polar force, so that the middle aromatic hydrocarbons were partially exposed to the surface of the coal sample, showing the most obvious hydrophobic modification effect. In general, the compound reagent adsorbs in the form of single-layer adsorption and double-layer adsorption through electrostatic force and polar force to enhance the hydrophobicity of coal samples, and the adhesion force is greatly reduced after the action of the compound reagent, and the flotation efficiency is greatly improved.