Abstract: A mechanistic model of the molten core-concrete interaction (MCCI) process was described, and it was used to calculate and analyze the MCCI process of Daya Bay Nuclear Power Plant when the station blackout (SBO) accident, or large loss of coolant accident (LLOCA) with the failure of safety injection was happened. The calculation results of this procedure were compared with the large-scale analysis program MELCOR to verify the reasonableness and correctness of the model. The results indicate that the model presented in this paper can simulate the MCCI process correctly and reasonably under the given severe accidents, and the calculation speed is fast. It can meet the application requirements of simulators.