Abstract: The molten corium-concrete interaction（MCCI） under severe accident（SA） is very important for the safety analysis of PWR. The chemical reaction in the MCCI process not only provides chemical energy as an important heat source to the heat transfer calculation, but also generates flammable gas（hydrogen and carbon monoxide）, which poses a threat to the integrity of the containment. Based on the independent developed SA code cosSA, this paper analyzed its chemical reaction model. Then, according to traditional million-kilowatt PWR model, this study calculated the MCCI process under severe accident condition, and evaluated the influence of chemical reaction process in the MCCI. The calculation results show that the chemical energy is about 20% of the heat transferred to corium-concrete interface, so that it has an important influence on the early heat transfer calculation on the MCCI, and the chemical reaction also produces a large amount of hydrogen which causes the burning progress in the containment, and leads to overpressure failure of the containment in the end.