Exploitation coalbed methane by gas injection is effective method of improving low permeability coalbed methane production. Coalbed reservoir is depleted, stress and strain of coalbed porous medium are changed because of changing of fluid pressure gradient, and result in effective permeability and porosity become lower, and production are decreased because of fluid-solid coupling effect. A dual porosity media fluid-solid coupling mathematical model of exploitation coalbed methane by gas injection is established. The nonlinear mathematical model is investigated by using finite different method and got some valuable conclusions: Improved recovery of methane from coalbed can be achieved by injection of carbon dioxide. There are two main mechanisms that aid recovery of the coal beds methane content. Firstly, by reducing the partial pressure of the methane present in the fracture, the diffusion from the coal is enhanced, the second mechanism is the competitive adsorption of carbon into the coal matrix. Molecules of CO2 preferentially absorb on to the surface adsorption sites, displacing methane, and exploitation coalbed methane by gas injection should note the fluid-solid coupling disadvantageous influence.