Abstract: Hydraulic measures were widely applied to the mining operation in the coal mine. In order to study a water injection affected to the seam gas desorption, a high pressure adsorption-water injection-desorption measuring and test device was applied to the measuring and test calculation on the coal to gas replacement deso rption value, pressure released desorption value and total gas desorption value under the condition of different adsorption balanced pressure and water content. The re sults showed that in the water injection process and within a period of time of the water injection, the gas pressure in the coal sample cylinder was in a continuously inc reasing tendency which could explain the injected water replaced the coal adsorbed gas. The higher water content was and the higher replaced desorption value would be.The max replaced value measured would be 11. 88 mL /g. After the pressure released, the gas desorption value of the water injected coal sample would be reduced. The higher water content was and the higher gas desorption value would highly reduced. The max reduction could be 68. 29%. After the water injection conducted, the t otal desorption value of the coal would be increased and thus the water injection could play a promotion role of the coal gas desorption.