Abstract: The core power capability verifications is an important part of the core design safety verifications. The method used in currently published papers is a synthesis method combining 1D and 2D computations, which is very conservative. Three-dimensional method for core power capability verification is still conservative as it can not tell how much margin there is. This paper introduces the methodology of the power capability verifications of the plants designed in CPR1000. The conservative of the methodology was demonstrated from the input assumptions and the calculation process, from this paper. It is suggested that the uncertainty should be reconsidered with a factor of 1.04 being removed for the input data. The operation domain should be decreased, and cases that would never occur could be deleted in the calculation. When the deviation value from nucleate boiling ratio exceeds the limit, the limits of operating domain and the uncertainty of hot channel factor for specific enthalpy rise could be reanalyzed to meet the safety requirements.