Selective flocculation flotation, selective oil agglomeration flotation, selective flocculation - gravity separation - flotation and other technologies are new ideas for solving refractory coal slime. The key lies in expanding the particle size difference between fine clay minerals and coal particles. The paper selects polyaluminum chloride (PAC), which has certain selectivity for kaolin and coal particles, as the research object. It explores the morphological characteristics of the Fe3O4 - PAC composite agent prepared by the sol - gel method and the solvothermal method, as well as its selective flocculation effects on kaolin and coal particles. Furthermore, it studies the influence law of the mass ratio of Fe3O4 and PAC in the composite agent on the difference in sedimentation characteristics between coal and kaolinite. The results show that PAC has selectivity for the flocculation of kaolin, and the best effect is achieved when its concentration is 3%. In the preparation of Fe3O4 particles, the solvothermal method is superior to the coprecipitation method. The Fe3O4 particles prepared by the solvothermal method are uniformly spherical with a small particle size. Both the precipitation method and the solvothermal method can prepare the Fe3O4 - PAC composite agent, and the one prepared by the solvothermal method performs better in terms of floc sedimentation rate and the transmittance of the supernatant of the solution. With the increase of the proportion of Fe3O4 in the composite agent, the sedimentation rate of kaolin flocs accelerates, but the amount of the agent required to form an obvious interface also increases.