Abstract: Efficient operation and life time management of power plants have become important issues in the nuclear industry. In particular, typical aging parameters such as stress and cumulative usage factor should be determined accurately for continued operation of a nuclear power plant beyond design life. However, most of the fatigue monitor-ing system was developed based on ASME code, which does not take into environment affect factor (EAF) of pipe. An effective fatigue evaluation methodology was suggested to meet the requirements on EAF analysis for new NPPs of RG 1.207 published by USNRC. The usefulness of the proposed fatigue evaluation methodology can be maximized by combining it with DCS data, and this combination will enhance the continued operations of old nuclear power plants.