Abstract: A coupled three-dimensional neutronics and thermal-hydraulics code NGFMN-K/COBRA-Ⅳ/COBRA-Ⅳ(NCC) was developed for PWR core transient analysis. The neutronics model was the NGFMN-K code based on nodal Green’s function method. One COBRA-Ⅳ sub-channel code was coupled with NGFMN-K implicitly for core transient calculation. Through integrating the other COBRA-Ⅳ code for sub-channel calculation on hot assemble, the code system was capable of evaluating safety-related parameters.The pin power distribution in hot assemble was constructed by P10H8B pin power reconstruction method. Numerical evaluation results on the NEACRP-L-335 C1 rod ejection benchmark problem show that the calculation results of NCC code agree well with reference solutions.NCC is capable of accident analysis.