Family letter archives are an important carrier of family history, with characteristics of originality and authenticity. Micro-history focuses its research on individual destiny and specific social groups, provides methodological guidance for the excavation and analysis of micro-historical materials such as letters and diaries, and provides a more vivid and specific interpretation for the historical narrative of specific time or space. This study centers on 113 letters of "correspondence between an old communists and her related social relations (1960——1997)", and collates the contents of the letters and completes the construction of the letter ontology based on the six conceptual categories of letters, characters, historical events, social events, periods, regions, and ethical contents and the corresponding hierarchical system. Then, combining micro-historical methods and social network analysis, this paper expounds the changes in the relationship between the character community and society, and shows the changes in the ethical structure and ethical orientation during the fifty years since the founding of thePeople's Republic of China from point to surface. The study reveals that the modernization process, especially the development of economy and technology, has promoted the transformation of traditional Chinese social ethics, mainly reflected in the rising status of industry ethics and the establishment of women's social attributes, but the family tradition still demonstrates strong resilience and internal stability.