Due to the shortage of conventional oil and gas resources, unconventional shale gas resources are becoming increasingly important so as to ensure the supply of global oil and gas resources. Shale gas mainly exists in organic shale and its interlayer, which are with ultra-low permeability and porosity. At present, carbon dioxide displacement is the most commonly used method to exploit shale gas. This method can not only improve the recovery of shale gas by replacing methane by adsorption, but also store a large amount of carbon dioxide in shale reservoir, thus slowing down greenhouse effect. To study the shale gas displacement by carbon dioxide, it is necessary to study the gas flow mechanism. In this chapter, on the basis of predecessors, considering various possible flow mechanisms, an apparent permeability model is established to describe the flow characteristics of methane-carbon dioxide two-component gas. Finally, the influence factors on two component gas permeability are analyzed to reveal the characteristics of apparent permeability.