The gangue in gob is a porous material that is generated by breaking the overburden layers. The key governing factor in studying gas flow in gob is the reaction law of void ratios to overburden movement. The evolution of the bearing capacity and void ratios of the gangue during the compression process is investigated in this article. The results show that the compression simulation of Voronoi Tyson and Grain growth blocks can transparently represent the gangue compression process. The contact force between blocks decreases as particle size decreases, while the amount of contact force increases. The strong force chain is illustrated as a "hourglass" and a "hyperbola" in the model. The void ratio of the block gangue combination of particle size decreases in a quadratic function /negatively correlated with the increase of compression. This study is of great significance to the judgment of gas enrichment area.