Abstract: Under the backdrop of climate change, the clustering of multiple hazards and the characteristics of disaster chains have become increasingly prominent. The current natural disaster investigation and assessment business system in China, which is dominated by a single disaster type, is no longer able to adapt to this challenge. Based on the development needs of investigation and assessment of natural disasters, especially major floods disasters in China, a systematic review of existing single disaster investigation and assessment technology systems and standard systems at home and abroad has been conducted. On this basis, it proposes a comprehensive framework for in-depth disaster investigation and assessment, clearly identifying cross-category disasters and the sequential relationships within disaster chains as the core objects of such assessments. Drawing upon field investigation data from the"7·20"extreme rainstorm disaster in Zhengzhou, Henan Province, and the"23·7"basin-wide extreme flood event in the Haihe River, the proposed conceptual framework of in-depth investigation and assessment was used to identify cross category disasters and disaster chain relationships under different disaster scenarios by constructing network topology, and the role of key disaster carriers and hidden dangers in the disaster transmission network was identified, which can provide a new perspective for disaster chain research and provide a reference basis for the investigation and assessment of large-scale regional natural disasters represented by watershed floods.