Abstract: The gas emission characteristics of coal is one of the key indicators to characterize the coal and gas outburst risk. The initial gas emission velocity ΔP of coal varies greatly with different metamorphic degrees.In order to analyze its internal influence mechanism, the N2 adsorption method and CO2 adsorption method were used to analyze the pore size of coal with different metamorphic degrees, and the effects of the specific surface area, volume and average diameter of macropore, mesopore and micropore pores on ΔP were studied. The results show that ΔP increases linearly with the increase of Langmuir volume, and has nothing to do with Langmuir pressure; ΔP increases with the power function of the specific surface area of the micropores, and ΔP is positively related to the volume of macropore, mesopore and micropore and the average pore diameter.Volatile matter is approximately in a power function relationship with Langmuir volume, and is in a negative exponential relationship with ΔP. The micropore specific surface area, the volume of the micropores, and the average diameter of the micropores are the main parameters affecting ΔP.Therefore, ΔP tends to increase as the degree of metamorphism increases, which is mainly affected by the development of micropores in coal.