Due to the special physical and mechanical properties and gas production mechanism of coal reservoirs, the changes of their physical properties are different from those of conventional reservoirs during the coalbed methane development process, of which the dynamic change in permeability is the most significant. During the development process of coalbed methane, production pressure difference can promote gas desorption, but meanwhile, it brings serious damage on coal permeability. This study simulated this damage caused by increasing the displacement pressure difference. Results indicate that the permeability of Duanshi and Gaohe samples declined about 71 and 63.3%, respectively, after the displacement pressure difference increasing to 2.50 MPa. Moreover, there was a critical value of pressure decline of coal. When the displacement pressure difference was lower than the value, the permeability would not change. Therefore, it would be best to control the production pressure difference lower than the critical value of pressure decline during the development. If exceeded, a reasonable production system to decrease the damage and to promote forming a high and stable production of a gas well should be adopted.