Abstract: Based on the gas drainage practice experiences with an open hole completion of the surface coal bed methane well, the seam gas drainage production i ncreasing mechanism with the cavity completion borehole through seam in underground mine was discussed and the cavity technology and the noted items of the boreh ole through the soft and outburst seam were analyzed.A site test and investigation was conducted in Hulu Sitai Mining Area.The test results showed that the cavity com pletion borehole through the seam could enlarge the influence scope of the drainage borehole, improve the gas drainage production, prolong the effective drainage time of the borehole and have other advantages.Within the 200 days' drainage period, the gas drainage quantity with the cavity completion borehole through seam would be 6.6 times higher than the borehole through seam.After 200 days' gas drainage, the gas drainage quantity with the cavity completion borehole through seam would be 6 1.6 m3/d and the gas drainage quantity with the borehole through seam would be 3.68 m3/d.