Abstract: This paper takes the super long gas drainage borehole in 16^# high gas coal seam with low gas permeability in Pinggou Coal Mine which is attached to Shenhua Wuhai Energy Company as the research object. By setting up the gas flow equation around the borehole and using the software of MATLAB, we obtain the approximate gas drainage radius of the ultra-long borehole. Then taking this radius as a reference value, we choose appropriate observation point to arrange test drilling that is perpendicular to the direction of ultra-long borehole in the return air roadway of the working face, and inject the gas of SF₆ in the testing borehole, and test the concentration of the SF₆ in the ultra-long borehole, and combine with the dichotomy to implement the concrete optimization steps to determine the final gas drainage radius of the ultra-long borehole.