The reliability is an important component part of research fields in power system. This paper presents an application of object oriented programming to develop reliability evaluation system of electric networks. A new approach to reliability evaluation and graph expression is proposed, and a computer aided decision making system of electric network reliability evaluation using Visual C++ 5.0 under Windows95 environment is developed. The system can provide reliability data for power system operation and plan, which is the foundation for operation and decision making. It has the characteristics of better expansibility, convenient usage, user friendly interfaces and so on.