Abstract: In order to adjust the trajectory of directional drilling according to the geological conditions in coal mine,a gamma logging while drilling tool for mining is designed,which integrates the formation natural radioactivity and trajectory measurement.In order to eliminate the influence of gamma detector on the azimuth of traject ory measurement,based on the basic principle of trajectory measurement,the influence characteristics of gamma detector on the azimuth measurement are analyzed by using finite element analysis and standard turntable test,and the influence correction model of azimuth is established by using generalized regression neural network (G RNN).The gamma detector has a certain influence on the magnetic field distribution around the inclinometer,and has different influence on the three components of the magnetic field in different directions. When the inclination angle and azimuth angle of the instrument are different,the degree of magnetic influence is also different,whic h affects the measurement accuracy of azimuth angle.After adding gamma detector to the back end of inclinometer,the azimuth error increases by 0.4 degree .After usin g the azimuth influence correction model based on GRNN,the mean square error of azimuth is reduced from 0.678 8 degree to 5.11x10-29degree.The accuracy of GRN N correction model is high,which eliminates the influence of gamma detector on the azimuth measurement of inclinometer.Based on theoretical analysis ,forward simulati on,experimental test and GRNN correction model,the correction method of gamma detector's influence on trajectory measurement azimuth is formed,which provides ref erence for solving the influence of other logging sensors on trajectory measurement.