Abstract: In view of the difficulty that gas extraction time of borehole along coal seam cannot be reasonably determined, the gas flow characteristics are analyzed based on the theory of coal rock mechanics and seepage mechanics, and then the control factors are determined. The gas density and gas flow in boreholes with different extraction time and combined effect area were compared. The results show that gas density of single-hole has obvious regional difference characteristics under the combined effect of goaf, residual coal pillar in the overlying coal seam and fault zone, and presents similar evolution law of unsteady rise and fall, large attenuation and stabilization stage in different regions. The gas flow of continuous boreholes presents attenuation law of negative exponential. The initial flow and attenuation coefficient are unstable when the main controlling factor is the permeability coefficient, and tend to be stable when the main controlling factor is the effective stress. The best effect is achieved within 60~120 day of extraction time. Meanwhile, the attenuation coefficient of gas extraction can be used as an auxiliary index to judge the difficulty of coal seam drainage.