Abstract: The directional drilling of coal mine is carried out in accordance with the pre-designed trajectory with the cooperation of the screw motor and inclinometer. The drilling trajectory can't be adjusted in real time according to the actual stratigraphic situation. The mine azimuth gamma logger while drilling can measure the radioactivity in real time, and can judge whether the drilling trajectory is in the target layer and provide the basis for adjusting the drilling trajectory in real time according to the changes of the formation radioactivity. The research and the realization of the mine electromagnetic wave azimuth gamma logging system (the name in safety standard is YSDGC) were discussed from the basic principle, the design of the key technology, the development, the experimental design and so on. The actual application of the system in underground coal mines was introduced. The system showed good azimuth gamma characteristics at stratigraphic interface, providing the basis for adjusting drilling trajectory according to the geological situation during directional drilling in underground coal mines.