Abstract: Hydro-cyclone can achieve a good separation effect in the production process,and has been widelyused in the field of coal preparation,but its separation mechanism is still in the research stage. In order to explore the working principle of the self-generating medium of the hydro-cyclone in the process of separation,this paper used the tricone angle cyclone to carry out the separation test of coarse coal slime,and conducted the simulation test of the tricone angle with Fluent software on the basis of the laboratory test data. Taking +0.2 mm slime as the sorting object and -0.2 mm fine coal as the sorting medium,the particle size composition of the intermediate material was controlled by adding fine coal of different particle sizes,and the law of its influence on the sorting index was analyzed. The simulation process of Fluent software used transient simulation. After obtaining a stable clear water flow field,the density field of the gas-liquid-solid three-phase was obtained by adding fine particles. The feed speed of the particles was set to 4.1 m/s,the turbulence intensity was 3.5%,and the equivalent diameter was 21.5 mm. The density field simulation turbulence model was an rsm model,the multiphase flow model used a mixture model,and the density of-0.2 mm particles was set to 1 700 kg/m³. The experimental results show that the addition of fine particle size will affect the ash content and yield of the overflow product of the three-cone angle cyclone,and the fine particle size as the medium will decrease,so will the ash content and yield of the overflow product. According to the cloud map of density field distribution simulated by FLUENT software,it can be found that the larger the fine particle size added in the cyclone sorting process,the larger the maximum density field value formed. Therefore,the density of overflow products obtained through sorting will also increase,that is,the ash content will increase. This indicates that the added fine particles can become the self-generating medium of the cyclone,forming the separation density field and promoting the separation.