Abstract: In order to explore the mechanical response mechanism of sandstone under different particle sizes and shear angles,Sigma 300 scanning electron microscope and MTS universal testing machine were used to carry out 9 groups of mechanical tests with different shear angles on three rock samples of medium sandstone,fine sandstone and siltstone with different particle sizes,and the mechanical response mechanism of sandstone under different shear angles was analyzed. The results show that: With the decrease of sandstone particle size,the shear strength increases significantly. The peak strength of fine sandstone and siltstone is 63. 27% and 89. 55% higher than that of medium sandstone,respectively. The peak strength of shear stress shows a “Z ” type change trend with the increase of shear angle,and the shear strength of fine sandstone is 14. 93 MPa,which is the most affected by shear angle. In addition,the turning point of sandstone peak strength moves forward with the decrease of particle size,and the turning angles of fine sandstone and siltstone are 0° ～ 10° and 20° ～ 30°earlier than those of medium sandstone,respectively. In the process of shear failure of sandstone,with the decrease of sandstone particle size,the increase of elastic energy of rock sample increases from 0. 39 to 1. 1,and the brittleness index increases from 0. 42 to 0. 55. The research results can provide a basis for the study of surrounding rock control technology of mine roadway.