Abstract: The size of coal particle had a certain effect on coal pore structure, which leaded to the change of coal gas adsorption performance. Based on the liquid nitrogen adsorption experiment of different particle size anthracite, we comparatively analyze the relationship between stage pore volume (stage pore surface area) and pore size distribution, and identify a certain relationship and explain the mechanism. The results showed that the larger particle size (10 mm, 6 mm) can not be a true reflection of the anthracite pore structure. The pore structure system encounters damage while anthracite particle size is 0.42 mm, especially for the diameter < 6 nm of pore. Anthracite particle size from 5 mm to 1 mm can be a true reflection of the anthracite pore structure. Diameter <6 nm of pore producing during microfissure crushing of sample communicating with microfissure and transferring to microfissure that diameter >6 nm leads to decrease of pore volume and surface area for diameter <6 nm of pore. On the other hand, the closed pore transfer into semi-closed pore or opened pore by pore throats splitting leads to the increase of pore volume and surface area for diameter >6 nm of pore.