ABSTRACT Aiming at the problem that coal gasification fine slag is difficult to float effectively, this paper combines flotation experiments and molecular simulation methods to study the mechanism of composite collectors on the flotation performance of gasification fine slag. In the aspect of molecular simulation, the quantum chemical characteristics of collector molecules and coal molecules in gasification fine slag were studied by density functional theory (DFT) calculation, and the electrostatic potential and frontier orbitals were calculated. Then, the flotation behavior of composite collectors in gasification fine slag was simulated by molecular dynamics. It was found that dodecane and dodecylamine had the best flotation effect as collectors. Finally, the flotation experiment verified that the recovery rate and other related indexes of gasification fine slag were better when dodecane and dodecylamine were used as collectors.