Abstract: By means of the discrete element software PFC, the waste rock compression model of coal mining area is established. Through analyzing the mechanical characteristics of different gradation schemes, we obtained that strata movement has a strong time effect and the loose coefficient of gangue can be reduced 15% to 24% from the earlier caving time to the compaction stability stage, and the particles block percentage of mining caving gangue is high, gangue lycopodium dispersion broken expansion coefficient changes more, required time of roof movement stability is longer. With continuous compaction of gangue lycopodium dispersion, lateral pressure coefficient increases, lateral expansion vertical load of pressure is up to a maximum of 65% to 83%, the swelling pressure is a serious threat to the mining empty area on both sides of the roadway, the greater of large size gangue percentage, the bigger influence on lateral pressure coefficient. Gangue dispersion in the compression process itself will rotate, rotating angle varied with different degrees of waste rock, but overall rotation range is from 0 to 360 degrees, and the small size of the waste rock rotation angle is larger.