Abstract: In order to find out the influence of methane adsorption on the pore structure of coal rock, a high rank coal sample was collected from southwestern China, and the methane adsorption under 30 ℃ with the maximum measurement pressure of 12 MPa was carried out, and the pore structure of the coal sample before and after the methane adsorption was also investigated with the low-pressure nitrogen adsorption and low-pressure carbon dioxide adsorption. The experimental results show that the isothermal adsorption of methane from high-rank coal exhibits the typical characteristics of rapid adsorption at low pressure, and the excess adsorption of coal and rock decreases after the excess adsorption reaches the maximum value; after methane adsorption, the adsorption hysteresis loop of low temperature liquid nitrogen decreases, and the adsorption amount of low temperature carbon dioxide also decreases, indicating that the pore structure of coal rock changes after methane adsorption; after methane adsorption, the pore volume and specific surface area of micropores, mesopores and macropores in coal rocks all decreased, especially the micropores and specific surface area decreased obviously, and the decrease of pore volume and specific surface area of different pore sizes has segmentation effect, which is mainly due to the decrease of pore volume and specific surface area of micropores with pore size less than 1 nm and mesopores with pore size less than 8 nm; the change of pore structure of high rank coal is related to the higher test pressure of methane adsorption.