In response to the urgent needs of safe operation and collision avoidance for high-density drones in the context of low-altitude economy,this paper proposes a fast path planning algorithm without conflict for multiple drones based on the fusion of prime factorization and Cooperative A* (Prime-Factor-based Cooperative A* ,PF-CA* ).The algorithm is to integrate prime factorization with Hadamard product operations to achieve millisecond-level conflict detection among drones amid flight,and design a local path planning method based on altitude adjustment.Moreover,the reservation table mechanism of the CA* algorithm is improved.On the basis of ensuring the optimality of the initial pre-flight path,the overlap degree of the initial paths of multiple drones is reduced.A third-order Bezier smooth curve library is designed.In combination of the action characteristics of the pre-takeoff planned path,turning points are identified,and efficient smoothing processing of the path is realized.The simulation results show that the path planning without conflict based on this method is characterized by optimal path planning,low overlap degree,and high real-time performance.Within a 5 km × 5 km airspace,the single-cluster operation success rate of hundreds of drones is over 90%.This method can provide a solution to the path planning problem of multiple drones in complex urban low-altitude airspace.