Abstract: In view of the design characteristics of marine nuclear power plant (MNPP), the technical scheme feasibility of molten pool material in-vessel retention (IVR) by external reactor vessel cooling (ERVC) method under severe accident was discussed. According to the lower power density and small lower head size of MNPP, the ERVC-IVR theory model and analysis code, named SR-IVR, were developed, which were testified with the benchmark problem. The results show that the model and code are suitable for the IVR analysis of MNPP under severe accident.