Abstract: In order to analyze the effect of particle size on coal porosity, coal samples from a coal mine with three different particle sizes were crushed and sieved to carry out mercury intrusion experiment. The results show that: the distribution curve of phase pore volume conforms to Gauss function and the distribution curve of specific surface area conforms to Power function; the pore volume has a correlation with the specific surface area, and the correlation decreases with the increase of pore size, the reason of this phenomenon is that there are micro fissures in the coal sample; the essential reason of the particle size affecting coal pore volume is that the partial size changes the size of the intergranular pore volume, and the intragranular pore volume does not change with the particle size; the pore volume and specific surface area of the coal whose pore diameter is less than 1 000 nm has obvious fractal characteristics.