As the core carrier for Urban Air Mobility (UAM), the performance of the electric powertrain in electric vertical takeoff and landing (eVTOL) aircraft directly dictates the vehicle''s payload capacity, flight envelope, and safety. To address the fundamental trade-off between power density and reliability induced by stringent mass constraints across diverse flight modes, this paper systematically reviews the latest technological advancements in this field. First, the "propeller-coupling system-motor" architecture is defined, and the characteristics and application boundaries of three mainstream propulsion configurations are compared. Second, the core performance limits and evolutionary trajectories of high-power-density motors and advanced carbon-fiber propellers are analyzed. Furthermore, the underlying mechanical-electrical-thermal multiphysics coupling mechanisms within the powertrain are revealed, elucidating the critical necessity of Multidisciplinary Design Optimization (MDO). Finally, current industrialization bottlenecks are evaluated and future trends are prospected, providing theoretical references and engineering guidelines for the architectural selection and technological breakthroughs of next-generation eVTOL powertrains.