Focusing on portability and extensibility requirements of civil aircraft power supply system embedded software, a object-oriented design method based on Unified Modeling Language (UML) was put forward. Considering the issues of the long cycle and high cost of software development, we adopted the hierarchical plug-in design method. According to the development process of UML design, the use case diagram of system requirement was established, the static structure model of logical framework and dynamic behavior model of logical framework were established for the software. Power supply system management of out-put was implemented via health monitoring of power supply system in real-time. Practical application showed that: 1) The embedded software has good portability and extensibility; 2) The independent design of software and hardware can shorten system development cycle and reduce the cost; and 3) The system design can implement health management of itself.