During the Warring States Period, the strength of a state determined the outcome of military conflicts, which led all states to focus on establishing the household registration system as the main source of tax revenue. This paper explores the significance of the Qin State’s emphasis on constructing the household registration system from four dimensions: the historical background of strengthening the household registration system during the Shang Yang Reforms, the construction and social functions of the household registration system, the relationship between the household registration system and the military merit system, and the integration of ethnic groups and resources through the household registration system. By discussing the legal transformation of the identities of Qin citizens and households from “unequal” to “equal”, and the combination of “household” and “register” management with the military merit system and the functions of rural society, the household registration system provided a solid social foundation for the military merit system and the integration and management of the grassroots society in the Qin State. This led to the integration of ethnic groups and effective resource integration in various regions before and after the unification of Qin, playing a significant role in the unification of the Qin Dynasty and having important implications for the formation and development of the multi-ethnic unity of the Chinese nation.