At the beginning and ending points of large-space height descent trajectory, airborne loitering munitions will oscillate severely and the transition time lasts too long. By researching the height-continuous and the velocity-continuous project trajectory, the physical reasons of those phenomena were analyzed. A novel trajectory for height descent with vertical acceleration being continuous was designed based on trajectory optimization. This height descent project trajectory can realize smooth and quick transition between different trajectories without changing the control system, and it also reduces height overshooting of the loitering munitions. An example was given, validating the effect of this trajectory design method, and it will provide reference for trajectory design of airborne loitering munitions and other similar munitions.