Abstract: Seam No.8 in Wolonghu Mine of North Anhui Coal Power Group is a seam prone to gas outburst. In order to remove the gas outburst risk from the seam, to effectively decrease the gas content and pressure in the seam, gas pre-drainage is adopted by using in-seam boreholes. According to the special requirements for drilling in-seam boreholes,multiple improvement has been performed with respect to the equipment, rod, tools required for drilling in-seam boreholes. Through great amount of field test and trial application, the drilling efficiency of in-seam borehole has been greatly improved. The frequency of blowout and attracting drill string during drilling has been reduced, decreasing drilling cost. It has good promotion prospect in similar mines.