For serial hybrid-electric aircraft (HEA), the flight performance of the whole aircraft was analyzed in combination with the dynamic characteristics within the given mission profile, and the overall parameters were associated with power and energy demand in each flight stage, assisting in design and sizing of each system component. Then, the calculation logic and each work path for the serial hybrid electric propulsion (HEP) system were summarized to explore the potential impact of energy management strategy (EMS) on the sizing method. Based on the established design system, a Dornier Do 228NG aircraft was selected and applied to compare the proposed method with that developed by two European teams from three design aspects. The results showed that the relative error for design point was less than 1.5%, the errors for conventional powertrain design were under 6%, and the evaluation of maximum takeoff mass (MTOM) for serial HEP design was less than 4% error. And it can verify the feasibility and effectiveness of our method. The characteristics, advantages and disadvantages of four EMS were analyzed and discussed. And based on an existing serial HEA, the Panthera Hybrid, the differences of power system working situation and design parameters under distinct strategies were studied and summarized. The results indicated that the MTOM under Light strategy was the smallest, and the benefits lied in that the maximum power demand during the take-off was taken by the fuel and battery power system at the same time, which optimized the power system weight directly. © 2023 BUAA Press. All rights reserved.