To evaluate different power distribution architectures of a pure-electric hybrid VTOL fixed-wing UAV for mountainous transmission-line inspection missions, a scenario-based flight profile including vertical takeoff and landing, hovering inspection, fixed-wing cruise, and mode transition was established. A system-level coupled analysis framework integrating the required thrust model, propulsion system model, power cable model, and battery model was developed. Based on propulsion subsystem validation tests, three power distribution architectures, namely hierarchical distribution, centralized distribution, and distributed power supply, were designed and comparatively evaluated under the same mission profile. The results demonstrate that the proposed model can accurately capture the variations in rotational speed, torque, current, and input power under different thrust conditions. The mode transition stage represents the most demanding high-power and high-current operating condition of the propulsion system. Compared with hierarchical distribution scheme A, distributed power supply scheme C reduces the average voltage drop, average power loss, cumulative energy loss, and average transition-stage power loss by 42.03%, 71.16%, 71.27%, and 76.67%, respectively, while increasing the end-of-mission state of charge (SOC) by 0.26 percentage points and improving the remaining energy margin after mission completion. The proposed task-driven evaluation framework enables the identification of peak-load conditions and high-loss power transmission paths during the preliminary vehicle design stage, providing quantitative guidance for bus segmentation, cable sizing, battery pack layout, and power-supply safety margin design of hybrid VTOL fixed-wing UAVs for mountainous transmission-line inspection missions in China.