Abstract: We analyzed the impact of the geomagnetic gradient on aircraft magnetic filed,and solved the aircraft magnetic filed model with flight test data of aircraft magnetic compensation and calculated value of geomagnetic gradient.The solving results of considering geomagnetic gradient and without considering geomagnetic gradient were compared.Then the compensation simulation test of interference magnetic field was carried out,and the interference magnetic field was caused by tumble,pitch and yaw of aircraft in 0°,90°,180°,270°courses.The results of simulation show that absolute error of model coefficient caused by geomagnetic gradient can reach as large as 5.24,and the improve rate(IR) will reduce 35.3%.