Abstract: In order to study the particle size distribution of drillings which were cut from coal with different hardness by reverse circulation sampling bit, reverse circulation sampling and orifice air sampling were compared by using the method of field test and laboratory measurement. The results are as follows: the hardness of the coal seam at the sampling position can be truly reflected by the strength factor of coal drillings which were obtained by reverse circulation sampling. The particle size distribution of drillings cut by reverse circulation sampling is independent of the sampling depth, but it is related to the structure of the drill bit teeth. For coal seams with different f values, the mass fraction of different particle sizes coal samples obtained from the same sampling drill bit is slightly different, but the distribution of particle sizes is roughly the same.