Abstract: Experiments were conducted on natural,water-saturated and water-gas-saturated coal samples to compare their mechanics.The results indicate that elasticity modulus,compression strength and volume compress coefficient of natural coal samples are larger than those of water-saturated coal samples and the latter are larger than those of water-gas saturated coal samples .However,their poisson’s ratios are opposite,and strains of parallel layer direction are larger than that of vertical layer orientation.The swelling experiments demonstrated that coal volume swells when it adsorbs gas and/or water medium ,and the coal rock strength and mechanical energy decreases. It was pointed that coal matrixes will shrink continuously, the coal reservoir mechanical intensity will gradually increase, and the poisson’s ratio and the plane stress ponderance of the covering stratum gravity will decrease,and the coal reservoir permeability may be improved with the discharging of water and gas medium during the coal bed methane recovery in ground wells.