Abstract: For the problems of drilling difficulties in soft coal seam, shallow hole depth and low hole formation rate, on the basis of extensive research of domestic related technology, we use soft coal drill rig and overall milling type outer spiral drill pipe to carry on composite slag discharge drilling by compounding air pressure. The complete drill rig integrated the drilling parameters monitoring, drilling hole dust removal and composite slag discharge. The coal field industrial test showed that the complete drill rig was reliable, greatly improved the drilling depth and hole-forming rate in soft coal seam.