Abstract: In recent years, the marriage and residence pattern of "two families merged into one" prevails in the rural areas of southern Jiangsu Province, which occurs in the one-child family structure. From the perspective of the transformation of family reproduction mode, this paper selects rural areas in southern Jiangsu province as the field research site, combs the changes of family reproduction mode, which starts with the interaction between family structure, family function and family ethics. Also, this paper explains the practice form, generation logic and formation mechanism of the marriage and residence pattern of "two families merged into one". It is found that the marriage and residence pattern of "two families merged into one" is a new model of marriage and residence emerging with the process of urbanization, which emphasizes both the ethical orientation of simple family reproduction and the functional orientation of expanded family reproduction. In fact, it is a practical model of family reproduction with both function and ethics in the transition stage. This paper discusses the influence of cultural characteristics and economic rationality of the marriage and residence pattern of "two families merged into one" on social existence, such as competition for grandchild's surname, differentiated care of original family and "generational inheritance" of property, stability of family marriage, power intervention of original family and adaptation of policy environment.