Abstract: Based on the study of coalfield geology and coal petrology, using field emission scanning electron microscopy(FESEM) as the main observation method, nanoscale pore research on coals was carried out for different regions, different geological ages and different metamorphic degrees. The results show that gas pores in coal are the pores left by coalbed methane(gas) generation, accumulation and escape during coal metamorphism, are secondary porosity. The pore diameter is mainly at nanometer size and round shape, with uneven density and distribution. The gas pore is intensive, often forms gas pore group, gas pore zone and gas pore nest. The gas pore development was affected by many factors. The macerals were the main internal factors. The thermal change rate was an important external factor. The degree of metamorphism was also one of the influence factors. According to the microscopic visibility, the degree of the gas pore development is described as developmental and undeveloped. Dense gas pore is common in the former, and sparse gas pore is occasionally or has no parallel in the latter. According to the degree of gas pore development, the gas generation mode and potential of the coal reservoir can be evaluated. The higher the degree of gas pore development is, the greater the gas generation potential is.