For the need of the research on continuous flow method to forecast coal and gas outburst in coal roadway,based on Darcy’s seepage law,the characteristics of dynamic gas emission from borehole wall in the drilling process were analyzed,and then under some simplifications and hypothesis,a Mohr-Coulomb cylinder seepage model about dynamic gas emission from borehole wall was founded using FLAC3D.The results of research show that the emission velocity of gas from borehole wall increases continuously with the depth of drilling increasing and is up to the maximum at the moment of stopping drilling,the accumulative total gas emission from borehole wall increases with drilling.