An on-line computerized system for balance-of-plant performance monitoring and analysis has been developed at the Institute of Nuclear Energy Research. This system was developed on an IBM PC/AT and implemented at Taiwan Power Company’s Chinshan nuclear power station. Test data acquisition and processing, as well as on-line performance monitoring and analysis, are the major functions of the system. The whole system is actuated on an integrated, menu-driven environment presented in either a Chinese or an English mode. It can carry out turbine cycle performance monitoring and analysis during normal operation. It yields cost-benefit analysis results of component degradation after finding out the thermal deficiency or lost power generation problems.