Coupled with isothermal adsorption and the Steele potential function, the characteristics of nanopores and their impact on methane adsorption and diffusion in low to medium-rank tectonically deformed coals (TDCs) were revealed by high-pressure mercury intrusion and low-pressure N-2/CO2 gas adsorption. The specific surface area (SSA) of low to medium TDCs is mainly provided by micropores (<2 nm, 96.64-99.56%), and the pore volume is mainly provided by macropores (>50 nm, 99.68-99.91%). The fractal characteristics of nanopores can be divided into four groups, i.e., D-1 (>100 nm), D-2 (<100 nm), D-3 (>8 nm), and D-4 (<8 nm). For primary coals and brittle deformed coals, D-1 > D-2, indicating that the heterogeneity of seepage pores is stronger than that of adsorption pores. For scaly coals, D-2 approximate to D-1, demonstrating the close heterogeneity and connectivity in adsorption and seepage pores, which are beneficial for coalbed methane (CBM) desorption and diffusion. However, D-2 > D-1 for wrinkle and mylonitic coals, indicating a stronger heterogeneity in adsorption pores than seepage pores, especially for mylonitic coal D-4 gradually increases with the enhancement of tectonic deformation, and D-3 shows a sharp increase in wrinkle coals. D-2, D-4, and SSA (<8 nm) all have a better positive correlation with the maximum adsorption capacity (R-2 = 0.57, 0.54, and 0.76, respectively), indicating that pores <8 nm in size have a dominant role in the adsorption capacity. With abundant activated desorption pores (0.7-1.5 nm), the content of schistose coals is between the contents, of configuration diffusion pores (0.5-0.7 nm) and Knudsen diffusion pores (>1.5 nm). Schistose coals are good CBM reservoirs, followed by the scaly coals. Lacking activated desorption pores and Knudsen diffusion pores, wrinkle and mylonitic coals have a high incidence of coal and gas outburst.