In order to reduce the ash content of raw coal and the environmental damage caused by gangue upgrading, and liberate the sluggish coal resources under buildings, rivers and villages, a set of underground raw coal washing-gangue filling system was established. The first gangue filling face 12212 of Xingdong Coal Mine was taken as an example, the underground gangue separation and filling technology were introduced. Field application showed that the separation and filling of underground gangue could reduce the emission of gangue and control the land subsidence. The economic and social benefits were considerable.