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. Currently, there are primarily four internationally recognized methods or systems for core damage assessment, which are mainly based on important monitoring parameters to provide qualitative judgment or quantitative analysis of the damage status. However, as a dock type floating nuclear power plant (FNPP), ACP100S has the characteristics of compact layout, limited instruments, and low power. The original core damage assessment methods or systems are not fully applicable to ACP100S. Therefore, it is necessary to determine the core damage assessment method based on the characteristics of the ACP100S reactor, such as severe accident progress, characteristics of instrument monitoring, and compact layout. For these reasons, a systematic study of the relationship between ACP100S 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 of important monitoring parameters for ACP100S reactor are proposed, based on a comprehensive consideration of the severe accident process and the characteristics of instrument monitoring. This method 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 ACP100S.