Abstract: Coal seam water injection has a remarkable effect on outburst prevention. Pore characteristic of coal seam is an important factor affecting gas adsorption / desorption and seepage. In order to research the influence of coal seam wa-ter injection on methane adsorption / desorption characteristics from the pore point of view,the ji15 -12070 face in Shous-han mine was selected for coal seam water injection experiment. The nitrogen adsorption method was used to study the pore characteristics of each coal sample and the fractal theory was used to calculate pore roughness. Then the static volumetric method was used to measure the adsorption / desorption parameters. The results show that the pore volume of each pore section increases after water injection,and the injection pressure has a positive correlation with specific sur-face area,pore volume and fractal dimension. Methane absorption / desorption hysteresis appears in each coal sample, and the higher the injection pressure is,the stronger the methane adsorption capacity is,and the greater the desorption hysteresis is. The number of pores and the roughness will increase with the increase of coal seam water injection pres-sure,it tends to retain more gas.