An outer-rotating motor is suitable in the industrial field for personal air vehicles because of its high torque and inertia characteristics. In the present study, the thermal performances of the outer-rotating 150 kW motor were evaluated numerically using computational fluid dynamics with various outer fins on the rotor. The simulation adopted the 3-D full-scale complex geometry of motor components, external airflow, and coolant conditions to describe the actual geometry and operating conditions. The Joule heating by current and resistance was also considered when rating operation conditions as a volumetric heat source in coils. The magnet and stator heat sources were calculated considering the motor's electromagnetic characteristics, and the bearing's mechanical loss was adopted as the heating value. The various types of fin arrays with inclined angles were simulated based on the numerical methods to obtain the differences in thermal performances. The mechanical efficiency of the motor was also considered because an outer fin is a flow resistance by rotating on the rotor surface. The 30 degrees of inclined angle of the outer fins have the best thermal performance and mechanical efficiency when 2 m/s of the axial flow condition. As a result, 0.23% of motor efficiency can be increased with an inclined fin angle without additional cooling conditions.