The role of micro-nano-scale stimulation of coalbed methane (CBM) reservoir is to open the fracture and pore channels, improve gas desorption and migration capabilities, and thereby increase CBM production capacity. Based on hydraulic fracturing simulation experiments, combined with liquid nitrogen absorption (LNA) and mercury intrusion porosity (MIP) measurements, the micro-nano-scale pore structure of coal before and after hydraulic fracturing stimulation in coal reservoirs was studied. It is found that significant changes in the number of pores in different pore sizes are the main reason for the changes in coal pore volume (PV) and pore specific surface area (PSSA) after hydraulic fracturing. the micro-nano-scale pore stimulation of hydraulic fracturing includes two forms of pore fragmentation and pore deformation, the coal with larger elastic modulus is mainly manifested as brittle crush. Moreover, larger in-situ stress will inhibit pore fracture and expansion, and even cause further compression of pores.