Aiming at the prominent issues of insufficient scenario adaptability and inadequate multi-constraint coupled modeling in electric vertical take-off and landing (eVTOL) operations within complex urban low-altitude airspace, a universal three-dimensional eVTOL flight path planning method integrating diverse mission scenarios and multi-objective optimization was proposed. Firstly, an optimized structured airspace planning framework was proposed to balance the contradiction between aircraft operation safety and airspace capacity in low-altitude airspace and ensure the efficient utilization of airspace resources. Secondly, based on the flight dynamics and aerodynamic characteristics of the rotor eVTOL aircraft, an accurate energy consumption evaluation model was established to further optimize the flight path. Through the construction of standard atmospheric models and obstacle zone environmental modeling, comprehensive optimization of path energy consumption, path length, path smoothness, and computational time was achieved, forming a holistic comprehensive cost evaluation function. Finally, based on the improved particle swarm optimization algorithm, a three-dimensional general path planning algorithm suitable for different operating scenarios and able to cope with various traffic activities was proposed. Simulation verification demonstrates that this universal 3D global path planning method can generate safe, feasible, and environmentally friendly flight paths for different mission requirements across multiple complex scenarios. Compared with traditional path planning algorithms, the improved method exhibits superior performance in energy efficiency and range optimization in typical urban scenarios, while demonstrating significant computational efficiency improvements in generating emergency paths for extreme urgent mission scenarios. The research outcomes provide a safety-economic balanced solution for urban air mobility system design, with its multi-scenario adaptability contributing to the development of multidimensional transportation networks and offering technical support for the low-altitude economy industrial chain development.