For launch vehicle, great testability design can effectively shorten launch flow and increase launch success rate. BIT（buildin test） is an important technique to improve the testability, maintainability and fault diagnosis of capability performance of a system or equipment. In this paper, analysis of the feasibility of BIT for launch vehicle electrical system and the design process and method of BIT is proposed, based on the background of new generation launch vehicle XX5. The purpose of this paper is to establish a standard set of BIT design process for launch vehicle electrical system, as the basis for Optimizing testing process and shortening the test cycle.