Nuclear power company plant maintenance has been conservative since it was born. Before we adopted DREAMS system, most of PM documents were handled with paperwork and we spent much time to perform plant maintenance. Last year KHNP constructed and implemented the computerized PM system, which was part of SAP system named DREAMS, and it made KHNP cut down expenses, save time, decrease trouble and optimize work intervals. To make PM system much better, we are trying to import equipment reliability process and we have a plan to initiate it within a year. Therefore the purpose of this paper is not only introducing an advanced methodology of plant maintenance, but showing the optimized PM system (equipment reliability process), considering safety and cost-effectiveness simultaneously.