With the increasing pressure to reduce carbon emissions and achieve sustainable aviation, aircraft electrification has become an important research direction for the development of future aerospace propulsion systems. Compared with conventional fuel-based aero engines, electric propulsion systems offer potential advantages in energy conversion efficiency, local emission reduction, noise control, and system integration. However, the practical application of electric propulsion in aviation still faces numerous challenges, particularly in terms of power density, energy storage, thermal management, and overall system architecture. This thesis focuses on the electrification of aircraft propulsion systems and reviews the key technologies associated with electric propulsion aero engines. First, the main electrified propulsion configurations are introduced, including hybrid electric, turboelectric, and fully electric aircraft.