Separation of solid particles in fluidized catalytic cracking slurry oil (SLO) is a tricky task because of their distinctive composition. Centrifugation and the oil-water interface method were used to separate solid particles in SLO. The results indicated that the oil-water interface method was better in particle separation. For instance, about 10 wt % fine coke powders can be separated by the oil-water interface method instead of centrifugation at the same conditions. Two different types of solid particles after ethanol/toluene extraction, i.e., catalyst fines and coke powders, were taken to investigate the composition of bulk solid particles. It was found that bulk solid particles were inborn coated by carbonaceous components rich in oxygenates and then modified by hydrogen-rich chemisorbed organics. The mechanism of particle agglomeration and separation by the oil-water interface method was proposed. Since water is cheap and accessible, this study could provide a green and efficient way for fine solid particle separation in SLO.