Abstract: The size of the coal particle had a certain effect on coal pore structure, which leaded to the change of coal gas adsorption performance. Based on the low-temperature nitrogen adsorption experiment of fat coal and gas coal, through analyzing the influence of the coal particle size on the pore volume, pore surface area and pore size distribution, according to the relationship figure of pore volume and pore size distribution, it found out a certain law, then further studied the law of coal particle size influence on the pore structure, the results showed that: the lower limit of coal particle size impact was between 0.074~0.2 mm in diameter, while the impact upper limit might be greater than 3 mm, and the larger particle size would affect the pore structure to reflect the true value.