The invention provides a nuclear power plant design and operation support method and system. The method includes the following steps that: the reactor core of a reactor is designed; three-dimensionalreactor core power distribution information is obtained according to design parameters; a reactor core model is built, the state of the reactor core is monitored and predicted in real time, and the reactor core model is amended according to stages; the calculation model of a spent fuel pool is constructed, so that the critical safety analysis calculation of the spent fuel pool can be performed, and nuclide tracking calculation is performed for an old fuel assembly; a spent fuel transportation container calculation model and a spent fuel storage container calculation model are constructed, so that the critical safety analysis calculation of a spent fuel transportation container and a spent fuel storage container can be performed; a reactor core source item model is built, the analysis and calculation of a primary loop source term and a secondary loop source term are performed, so that source item information can be obtained; and the calculation model of a reactor main shield is built, and ray measurement information in the reactor is calculated according to the calculation model. With the method and system of the invention adopted, design precision and operation reliability can be improved, and therefore, the safety and economy of a nuclear power plant can be improved.