The direct stress analysis method used for the fatigue analysis was proven to be effective and straight forward in application to fatigue monitoring system in nuclear power plants. The stress intensity factor obtained from the method using Green`s function and Duhamel`s integration have shown good agreement with those evaluated by the standard finite element analysis and will be used for the crack monitoring system. The fatigue monitoring program of K-FAMS was applied to YGN unit 1 surge line in heat up field operation and verified the application to a nuclear power plant. The real time fatigue monitoring system can give an important information on the life extension of the existing plants as well as the design improvement of the next power plants. (Author).