In response to the issue that traditional trajectory planning methods based on spatial dimensions are no longer suitable for modern, complex battlefield environments due to their relatively low planning density, this paper proposes a 4-dimensional (4D) trajectory planning method for high-density unmanned aerial vehicle (UAV) operation scenarios in modern urban environments. By introducing the time dimension, the 3D combat scenario is extended to a 4D dynamic airspace. With the objective of minimizing planning costs, the cost estimation function of the A* algorithm is restructured in the time dimension, resulting in the development of the 4D-A* dynamic path planning algorithm for urban warfare. Simulation results show that 4D-A* not only effectively enhances the collaborative combat capability of multiple UAVs in high-density operational environments but also avoids the inherent "detour" issues caused by the absence of the time dimension. It reduces time-related costs, while also demonstrating higher reliability and robustness compared to the basic method. In complex real-world scenarios, it can prevent the decoupling of spatial and temporal attributes, effectively avoid multi-vehicle conflicts, and reduce flight duration, thus meeting the mission requirements of UAVs in urban combat.