The filling material of gangue has a significance influence on the filling effect of primary gangue backfill mining, in order to improve the filling effect of primary gangue backfill mining, the compression mechanical experimental of gangue of different particle size and different gradation were done in laboratory. The experimental results show that the ability to resist compression of continuous graded gangue is the best, and the ability of discontinuous graded gangue is better than the single particle gangue; when using the discontinuous gradation plan, the ability to resist compression is the best when there are 30 percent fines; when using the continuous gradation plan, the ability to resist compression is the best when n=0.4. Based on the experimental results, in the process of gangue compression, the main effect of coarse material is add the fiction force during gangue particles mutual sliding, and the main effect of fines is filling the space between the gangue particles. Therefore, in order to improve the ability of gangue to resist compression, the coarse material and the fines should cooperate well, and this effectively improve the filling effect of primary gangue backfill mining.