Shale gas can occur in both the adsorbed state and the free state inside pores ranging in size from 10-6 to 10-9. This paper reports the results of research on the mechanisms and characteristics of gas transport in shale gas reservoirs, which deviates from Darcy's law. The gas migration process is divided into migration in organic and inorganic matrix pores based on Knudsen number. The new models that are proposed for various flow modes take account of the effect of adsorption-desorption, slippage, Knudsen diffusion, and water saturation. The new flow models were modified with due regard for adsorption-layer thickness and water-film thickness on the pore walls. The new model constructed for diffusion flow can be used in designing and developing shale gas reservoirs.