The focusing effect of the metal molten pool plays an important role in elevating the validity of the In-Vessel Retention (IVR) during a severe accident while the melting of the shroud and basket can contribute to the formation of the metal molten pool. Therefore, the study on the melting behavior of the shroud and basket can offer technical support for the validity analysis of IVR. The method of computational fluid dynamics (CFD) has been used to establish a two-dimensional calculation model of the 1/8 core of ACP1000 to study the melting behavior of the shroud and basket during the severe accident of large LOCA. The core has been divided into ten nodes in the axial direction and the radiation model and the solidification and melting model have been considered during the calculation. The results show that the shroud at six out of ten nodes and the basket at five out of ten nodes have melted totally before the first significant migration of the core and that the basket always starts to melt after the shroud has melted totally at the same node.