Abstract: The core degradation that results from loss of coolant, including core heat-up, cladding oxidation, and fuel damage and relocation, plays an important role on the integrity of containment and the behavior of fission products. The PHEBUS-FP program has been conducted by the French Institute de Radioprotection et de Sûreté Nucléaire (IRSN), studying the core degradation process and the behavior of fission product. PHEBUS FPT0, FPT1 and FPT2 were simulated using ATHLET-CD code in this paper, focusing on core heat-up, cladding oxidation, and fuel damage and relocation. The results indicate that different steam flows and different heating powers will lead to different core degradation processes, which are in good agreement with experimental data in tendency. And the model parameters in cladding oxidation and fuel relocation were analyzed to discuss the discrepancy of calculation results.