Abstract: Under different confining pressures, gas seepage tests are carried out, and these tests are used to discuss gas seepage mechanism in coal. The tested and theoretical results show that under different confining pressures, gas seepage laws are consistent in coal. In the higher gas pressure section, the percolation curve of Q and △2p/L meets the linear relationship, but the gas pressure is lower, the seepage curve of Q and △2p/L deviates linear relationship of Darcy’s law. The critical point lies from nonlinear to linear segment of gas flow in coal, and it is a gradual process from non-Darcy flow to Darcy flow. At high Reynolds number, gas percolation obeys Darcy’s law, but at low Reynolds number, the gas seepage in different metamorphic grade coals is non-Darcy flow. The collision of gas molecules and coal wall is the physical mechanism of gas non-Darcy flow phenomenon, which is determined by the mean free path of gas molecules and pore structure of coal, and the theoretical calculation well reveals the mechanism of gas non-Darcy seepage in coal.