Gas transport through coal matrix is generally assumed to be dominated by gas phase diffusion. However, the matrix pores contain a certain amount of water, which occupies the gas phase diffusion channels. Gas phase diffusion theory cannot be used to interpret the effect of water. This article studies the phase behavior and flow mechanisms in coal matrix. It concludes that the desorbed gas exists in matrix pores with two states: dissolved gas and free gas. Dissolved gas diffuses in water, and free gas flows into the cleats. These results provide a theoretical basis for well productivity prediction and well testing.