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The correct understanding of shale pore characteristics is the foundation of shale gas exploration and development. Comminution is an essential sample pretreatment in many measurements of shale pore characteristics, but little is known about the influence of comminution on shale pore characteristics. This study utilizes low-pressure nitrogen adsorption and helium porosity measurements to investigate the evolution of shale pore characteristics during comminution. The results show that reducing the proportion of inaccessible pores and improving the gas diffusion efficiency are the main effects of comminution on the shale pore characteristics, resulting in an increase in measured porosity. The recommended analytical shale particle size for low-pressure nitrogen adsorption and helium porosity measurements is below 80 and 20 mesh, respectively. The proportion of inaccessible pores in shale investigated in this study ranges from 13.11 to 45.89% and shows a negative correlation with thermal maturity and a positive correlation with clay content. This suggests an improvement of organic pore accessibility during thermal evolution and a high content of inaccessible pores in clay minerals.