Abstract: Baozhai was a type of defensive fortress which was common in rural China. Large numbers of this military fortress were built around the villages of northern China during the Ming??Qing periods, which reflected the social change in these areas. This article is a case study of Baozhai in Yu County, Hebei Province and illustrates its construction, types, functions, administration and the symbolic meaning as well as its influence on the situation along the frontier in northern China and the change of the weisou system. Meanwhile, we can observe the strength of the rural gentry and the transformation of the villagers?? conception during the evolution of Baozhai.