As traditional UAV trajectory planning algorithms generate redundant search points and poor real-time path planning in emergent threat scenarios， a dynamic trajectory planning algorithm for UAVs based on multi-factor Dubins path is proposed. First， the algorithm uses the traditional Dubins path to find effective path extension points based on the UAV’s own performance constraints and the location of the sudden threat area. Sencond， a path extension point evaluation function is established based on the path length and threat combined with heuristic search ideas. Finally， the path extension point is selected through the path evaluation function， and a better path is planned. The simulation results show that when the algorithm is used for trajectory planning in sudden threat scenarios， the path length is shorter and the path extension points are fewer， and it conforms to the change of the heading angle of the drone during the actual flight， which can effectively ensure the safety of the drone and real-time trajectory planning.