Abstract: In view of the problems of difficult drilling slag discharge, low drilling efficiency and difficulty in forming holes in the construction of hydrodynamic directional drilling in broken soft coal seams, analysis of the instability characteristics of boreholes in broken soft coal seams. According to the larger stirring volume of coal slag per unit of the drill pipe, the more conducive to spiral slag discharge, a composite slag discharge method with high spiral mechanical slag discharge as the main and hydraulic slag discharge as the auxiliary is proposed. The Φ98mm welded spiral drill pipe is developed, and the structural characteristics and slag discharge capacity of three specifications of spiral drill pipes are compared and analyzed.A field tests were carried out in Wangpo Mine and four boreholes with depth over 300 m were constructed.The test results showed that the drilling efficiency of Φ98 mm welded auger rods could reach 30.6 m/shift, and the amount of slag returned per unit footage can reach 270 kg/m, and the drilling efficiency and slag discharge capacity are more than doubled compared with Φ89 mm auger pipe and Φ89 mm triangular auger pipe, formation of directional drilling equipment and technology suitable for high-efficiency slag discharge in crushed and soft coal seams.