Based on two dimensional particle flow code (PFC^2D), a horizontal push-shear test model of coal waste is established to simulate the push-shear tests that gangue have different compactness before and after improvement reflected by different gradation and porosity. The pushing force-displacement curves of the coal waste specimens are reproduced and verified by the PFC^2D model, and the difference in the curves is analyzed. The law of particle mobilization in push-shear tests is verified from the perspective of mesomechanics. The results show that the contact force in the model will transmit along the slip surface. Distribution of contact force after improvement presents inverted crescent-type. Furthermore, the angle between the direction of contact force and the horizontal in the model after improvement becomes larger, and the contact force concentrates in a narrower area. The slip surface is also determined in push-shear tests by means of the displacement vector chart.