Based on the established experimental method of water injection coal samples and isothermal adsorption experiments to stimulate real reservoir conditions, the Isothermal Adsorption/Desorption System Model IS100 and Electrohydraulic Servo Rock System Model MTS815 are used as the main apparatuses to carry on injecting water in coals with different ranks under high pressure (8~20 MPa). The conclusion was drawn that liquid water of water injection coal have different influence on methane adsorption of different rank coals (0.46%