Abstract: With the coal rejects quantity continuously increased in the mine thin seam mining, the mine actual production capacity would be highly decreased.lf the coal preparation plant move and set up in the underground mine to prepare the coal in the underground mine, high social and economic benefits would be obtained.Thu s based on the coal preparation of the high coal reject content coal in China, the paper provided the conception of the coal separation in underground mine.①To chang e the traditional technique of the raw coal lifting to the surface for the coal rejects and coal separation and to have a coal preparation and coal rejects backilling integra tion in underground mine could solve the coal rejects pollution and goaf surface subsidence problems.②The application of the coal preparation system in underground mine would have a high efficient green mining mode with cleaned coal lifted to surface, coal rejects backfilling in the underground mine and mine water recycled in the u nderground mine.③The technical requirements of the flame proof, explosion proof, dust control, electrostatic prevention and others were provided for the equipment in order to let the coal preparation equipment meet the underground operation requirements.