Abstract: Hydraulic technology is widely used in gas control method, and hydraulic measures will enable coal to withstand the impact of wet-dry circulation and the impact parameters of coal. Experimental tests of coal firmness coefficient on different coal that collected from low gas coal seam, outburst coal seam and rock-burst coal seam under dry-wet circulation have been carried out. The influence laws of dry-wet circulation on coal firmness coefficient are obtained; and the deterioration effect of coal under the action of dry-wet circulation is analyzed. The results show that each coal firmness coefficient is reduced in varying degrees after alternating action of drying and wetting, the overall trend is that the number of f value is lower periodically with the increase of alternation frequency of wetting and drying.