When the aircraft files from one segment to the next one,it needs to judge whether the next segment is activated or not.In this paper,a new method is proposed for automatic activation of planned flight segment.By obtaining the current position and magnetic deviation of the aircraft,and combining with the longitude and latitude of magnetic difference of the corresponding positions of the adjacent three waypoints, the magnetic heading angles corresponding to the three waypoints and the aircraft position are calculated respectively.The difference between the magnetic heading angles is compared to determine whether it is activated or not.After the algorithm derivation is completed,the model is built based on SCADE SUITE,and the actual data sampling and simulation are carried out by using the JEPSSON chart.The simulation results show that:1) This method can activate the next segment stably and effectively;and 2) It is practical and effective,and is simpler in computation compared with the traditional methods.The method has been used successfully in actual flight and has achieved the expected effect.