Core damage assessment is primarily utilized for evaluating the consequences of severe accidents, and its accuracy play a very important role in emergency decision and emergency response. At present, there are primarily four internationally recognized methods or systems for core damage assessment, which are mainly based on important monitoring parameters, such as core exit thermocouple temperature (CET) and containment radiation level (CRM), to provide qualitative judgment or quantitative analysis of the damage status. However, there are three issues need to be concerned. Firstly, these methods or systems primarily address severe accident scenarios caused by large break loss-of-coolant accidents (LBLOCA). However, the ACP100 has eliminated the possibility of LBLOCA due to its integrated core design. Secondly, these methods or systems employ a proportional scaling approach in quantitative analysis, neglecting the trends in monitoring parameters between different status, which lead to relatively rough results. Thirdly, the recommendations for selecting results need to be further analyzed based on the characteristics of instrument monitoring. For these reasons, a systematic study of the relationship between ACP100 typical severe accident progress, important monitoring parameters and the state of the core has been calculated using the comprehensive severe accident analysis code ISAA. Core damage assessment method and calibration value recommendations for ACP100 reactor are proposed, based on a comprehensive consideration of the severe accident process and the characteristics of instrument monitoring. This method integrates the judgment logic of the TECDOC-955 and CDAG, providing a more refined assessment model and suggestions for result selection, which serves as an important basis for severe accident consequences and emergency response of ACP100.