This essay is a transcript of the lecture delivered in the Yunping Hall by Prof. Ming-Shih Kao for the student of the History Department of National Zhongxing University on December 18, 2014. It discussed the governing principle of Tang Dynasty, traditional social structure, the formation of a hierarchical society, the operation of the hierarchical system and its impact on later history. The Tang hierarchical society was constructed through imperial power according to the rite system(li, or proprieties, rituals). The status of all the subjects in the Empire were conferred by the Empire through the mechanism of two interwoven systems: the political power and social relations. These two kinds of relationship combined could show the hierarchical status of an individual. This hierarchical order was regulated by the contemporary laws and codes. Violators of this order was punishable by law. This practice was continued until the Song Dynasty. The only significant change was caused by the change of political position and status. Consequently, the change of the hierarchical society was also an important part of the Grand Tang-Song Transition.