The component-based software design method inherits and develops the object-oriented programming method. This paper not only presents the concept, character, principle and application of the method, but also describes a COM-based three-layer client/server software architecture. Concerned with the development of Fushun Distribution Network Information Management System (DNIMS), a new idea to design component-based software is introduced. Since to finish the development of DNIMS for every aspect at the same time is difficult, it is necessary to use the component-based software design method on the basis of uniform programming, so that the whole system can be implemented step by step. It has been practically proved that this approach can effectively enhance the reusability and expansibility of the software, and further can improve the reliability and maintainability of the system. Moreover the productivity of the software is increased obviously.