An improved A

*

algorithm is proposed to solve the problem that UAV can’t plan its trajectory in time and effectively in complex 3 D space. Firstly

flight pitch angle and yaw angle of the UAV are constrained to reduce the extended area of the track node. Secondly

in order to prevent being failed to detect condition of intersection of track and obstacle area in time

that terrain obstacle occur the danger factor is introduced and the search area near the node is detected

so as to improve the ability of the algorithm to predict the risk in advance. Finally

in order to meet the actual flight requirements of UAV

B-spline curve method is used to generate a continuous and smooth track. The simulation results show that the track planned by the impr

oved algorithm satisfies the constraints and has strong feasibility and robustness

and the degree of track safety is much higher than the traditional algorithm.