Abstract: Objective The coal gasification fine slag is rich in inorganic substances such as silicon and aluminum, as well as residual carbon. Method Aiming at the problem of carbon ash separation in gasification fine slags, taking flotation as the core, by optimizing the reagent system and process parameters, the enhancement mechanism of the composite collector on carbon ash separation was explored. Result&Conclusion Sample analyses show that the inorganic minerals are mainly in the form of crystalline quartz, mullite, and amorphous glass, while the residual carbon has a porous and flocculent structure and is closely interbedded with inorganic substances. Scanning electron microscopy and pore analyses indicate that the residual carbon has a high specific surface area (388.55 m²/g) and a complex pore structure, while the surface of glass microspheres is smooth and partially embedded in the carbon pores, making separation difficult. Flotation tests show that the combination of n-dodecane and n-decanoic acid as collectors has a better flotation effect than n-dodecane alone. Mechanism studies indicate that the composite reagent enhances the hydrophobicity of the carbon surface through physical adsorption: the negatively charged groups ionized from n-decanoic acid repel the negative charges on the inorganic surface, promoting the selective adsorption of the collector on carbon particles. Infrared spectroscopy shows that the composite reagent significantly weakens the intensity of the C-O-C peak, strengthening the effect of hydrophobic functional groups. Low-field nuclear magnetic resonance analysis further confirms that the composite reagent reduces the ineffective adsorption in micro-pores and optimizes the utilization efficiency of the reagent.