Abstract: In order to study the replacement effect of water to gas in coal, setting up the experimental platform, under the constant pressure of the experimental system, under different water contents and different adsorption equilibrium pressures, the experiment was studied. Results show that under the same adsorption equilibrium pressure, the replacement amount and the replacement rate increase with the extension of time, but the range is in constant decrease. The maximum amount and the maximum rate of replacement are positively correlated with the water content and the adsorption equilibrium pressure; under the same water content, the maximum amount of 1.5 MPa is smaller than that under 2.5 MPa, but the maximum rates of the two have little difference; the speed of replacement experiences three stages, including a rapid increase, slow lasting, decay to zero.