The gas desorption capacity is beneficial for predicting and optimizing gas recovery from coalbed methane reserves. In this study, coal samples were collected from the southern Qinshui Basin. The isothermal adsorption experiment and mercury injection capillary pressure test were adopted to study the gas desorption capacity and pore structure. The efficient desorption capacity definition was proposed to evaluate the efficient desorption stage. The results show that the micropores and transition pores are well developed in all of the coal samples. There are two fractal dimensions in coal: the percolation fractal dimension (D1) and the diffusion fractal dimension (D2). A larger pore volume and well-connected pore network facilitate efficient desorption and transport of methane, leading to an enhanced methane yield. D1 is positively correlated with efficient desorption capacity, while D2 has a weaker effect. In addition, the basic properties of coal samples, such as coal rank, vitrinite content, and inertinite content, also have a certain effect on the efficient desorption capacity, but the relationship is not clear. These findings enhance our understanding of coalbed methane desorption capacity.