Based on the established parameter files of the Chin-Shan and Lung-Men Nuclear Power Stations, the Modular Accident Analysis Program version 4.0.4 (MAAP 4.0.4) was used for steady state evaluation. Performing the steady-state simulations assure the appropriateness of the parameter files used for the MAAP calculations. The purpose of this study is to evaluate the postulated anticipated transient without scram (ATWS) severe accident scenarios for the Chin-Shan and Lung-Men Nuclear Power Stations. In this study, the behaviors of reactor core and containment, and release of fission products were analyzed. Besides, the phenomena associated these scenarios were discussed.