In recent years, with the rapid development of the new energy “three-electric” system (electric drive, motor, battery) and the continuous spillover of the low-altitude economy, the drive motor, as a core component of both, is advancing toward high power density, high torque density, high efficiency, and high energy savings. Compared to motors using traditional round copper wire for winding coils, employing flat copper wire can increase the slot fill factor by over 20%, enhance motor performance and efficiency, and reduce motor volume. Based on the design requirements for a drive motor in a specific new energy vehicle, this paper first considers field-weakening design under high-speed operation and designs a flat wire drive motor meeting performance requirements through theoretical calculations and Maxwell electromagnetic simulation. Simultaneously, the rotor structure was optimized, resulting in deformation far less than the air gap length at 12,000 rpm, fully satisfying operational demands. Then, the AC losses of the flat wire winding coils under different combinations of winding layers and parallel branches were comparatively analyzed. Finally, using co-simulation between optiSLang software and Maxwell and employing evolutionary algorithms, the motor structure was optimized. The optimized motor exhibited a 3.1% relative increase in output torque and a relative decrease in the harmonic amplitude of the no-load back EMF, demonstrating significant optimization effects.