Abstract: In order to effectively identify coal seam, roof and floor, mine electromagnetic LWD gamma logging tool was developed for directional drilling in coal mine. The calibration coefficient of the instrument can be obtained by natural gamma logging scale, and various measurement curves of mine electromagnetic LWD gamma logging tool can be obtained by standard well test and crossing borehole test in coal mine. Through comparing with the gamma curve of standard well and analyzing the geological data of the crossing borehole, the measurement result accuracy of mine electromagnetic LWD gamma logging tool is verified. The application test in underground coal mine shows that the mine electromagnetic LWD gamma logging tool can not only measure the drilling track, but also effectively identify the interface of coal seam roof and floor in directional drilling operation, which is of great significance for guiding the operation of directional drilling underground and improving the drilling encounter rate of target layer.