Aiming at the problem that the search path of A* algorithm is not smooth and does not have dynamic obstacle avoidance in 3D environment, this paper proposes a fusion A* algorithm. Based on the A* algorithm, this algorithm first introduces pitch angle and yaw angle as search constraints, which shortens the time for path planning, and secondly uses variable weight evaluation functions and UAV range, flight height, and threat cost Finally, the smoothed A* algorithm is combined with the artificial potential field method, and the particle swarm algorithm is used to optimize the parameters involved in the A* algorithm and the artificial potential field method. The simulation results show that compared with the traditional A* algorithm, the fusion algorithm saves 5.34% of fuel consumption, improves the search efficiency, shortens the path length, the planned path is smoother, and can achieve real-time dynamic obstacle avoidance.