Electric aircraft is a new type of aircraft, with extraordinary advantages of environment friendly, high efficiency, energy saving etc., which may have important impact on the future development of aviation, and a good prospect. Design methodology and techniques of electric aircraft are outlined in this paper. A brief introduction of the electric aircraft development since the 1970's is given firstly, followed by an analysis of its performance through related data, and its shortcomings. Then the conceptual design methodology of different types of electric aircraft (solar powered, battery powered, fuel cell powered, retrofitted) is summarized and analyzed in detail, together with related design tools and support systems. Specific techniques of electric aircraft design, including the aerodymanic configuration and the general layout, the electric propulsion system, the structure and the materials, are discussed finally.