In order to explore the feasibility of the application of cooking waste oil in the separation of difficult floated coal slime, －0.5 mm coal particles were used as the research object, and the coal samples were wetted with different media. The settling test was carried out in the waste oil-water two-phase system, and the settling behavior of coal particles in oil, water and oil-water mixed interface was observed and recorded. The settling velocity of coal particles when reaching the oil-water mixed interface was determined by image processing software. Through the final settling results and force analysis of coal particles, the conditions for the settling and separation of coal particles in waste oil and water were clarified. The effects of ash content, particle size and wetting of different media on the settling and separation of coal particles at the oil-water interface were systematically studied. The test results show that the settling and separation results of coal particles at the oil-water interface are positively correlated with the square of coal particle size and density, and negatively correlated with the dynamic equilibrium force at the oil-water interface. The coal particles treated by water wetting show different settling states, while the coal particles treated by oil wetting and unwetting (drying) are suspended on the oil-water mixed interface. Water wetting treatment can make the surface of coal particles adhere to water, reduce the dynamic equilibrium force between coal particles and oil-water interface, and realize particle settling and effective separation. In addition, the conditions of settling separation of coal particles in waste oil-water system were further verified by replacing waste oil. The research results provide new ideas and theoretical support for the application of waste oil in the efficient separation of coal slime.