Abstract: The foam drilling technology is a kind of effective construction method for long borehole along soft coal seam used for gas drainage in underground coal mine, which has lots of potential technical advantages compared with other drilling technologies, and the defoaming technique and matching equipment is the key to the popularization and application of foam drilling technology in soft coal seam. A kind of defoaming technique developed for foaming drilling technology used in underground coal mine was introduced in this paper, which used the compressed air as the dynamic medium and wall-jet as the single power source. Three kinds of defoaming technologies of chemical method, gas jet method and centrifugal field method were used simultaneously, so its significant characteristics were rapid and reliable. At the same time, the volume and weight of matching device were small, easy to move, no moving parts and electrical components, so it met the requirement of the drilling construction environment for explosion-proof in underground coal mine. Indoor and field tests achieved good results.