Coal gasification slag (CGS) presents significant challenge to the green and low-carbon development of the coal gasification industry due to its limited utilization restriction. In this study, cationic surfactant DTAB was used with kerosene to formulate an emulsion collector. The flotation results showed that, the increase in collector dosage could significantly improve the combustible recovery. At an optimal collector dosage of 10 kg/t, an increased DTAB ratio could significantly diminish the ash content of flotation concentrates and improve flotation precision. Through flotation dynamics experiments and fitting of the Fuerstenau upgrading curve, it confirmed that the entrainment of fine-grained particles with high ash content is the primary contributor to high ash content in flotation concentrates. Combined with FTIR spectroscopy, XPS and other analysis method, it validated that the surfactant effectively reduced the dispersed particle size of the agent, the increased contact angle of RC surface also improved hydrophobicity and improved particles hydrophobic agglomeration strength. Molecular dynamics simulation further illuminated that the surfactant covered part of the hydrophilic sites on the residue carbon (RC) surface and influenced the electrostatic interaction. The research results have important theoretical significance for perfecting the flotation theory of CGFS.