The research on Electrical-Powered Unmanned Aerial Vehicles(UAVs) Design is based on the theory of aircraft design. The assumptions and physical models in conventional aircraft design are revised for electrical-powered UAV design.The appropriate wing loading and power loading that can satisfy all performance requirements are determined clearly in the matching plot. According to flight time and payload requirements, the maximum take-off weight is formulated and estimated successfully. The electrical motor of the propulsion system would be appropriately selected with the power requirement. On the basis of the wing area, the aerodynamic design and stability design of electrical-powered UAV would be completed.The major contribution of the research is to propose a new electrical-powered UAV design procedure based on the drag polar model. Through the two parameters of the zero-lift drag coefficient and induced drag coefficient factor iteration, the design procedure would be completed. The new design procedure would reduce the number of iterations in the conceptual design and preliminary design phase. This method also has a practical physical meaning and can directly correspond to aircraft performance. After the design, composite materials are used to build the flying wing UAV. The successful flight tests verify the feasibility of this systems engineering approach for small electrical-powered UAV in the research.