In the process of history, the western society has formed a stable population community referred to as "nation" through population nationalization and national integration. At the same time, through the political revolution, the national sovereignty was transferred from the monarch to the national (nation), and then the nation-state (nation-state) was constructed. As a result, the nation not only obtains the form of the state, but also becomes a national community, which contains the mechanism of population nationalization and national integration in itself. Through the carding and analysis of the process of further enriching and perfecting the above mechanisms, this paper clarifies the interactive relationship between the nation and the modern state, and holds that the nation is the basic social and political mechanism of the modern state. On this basis, the author analyzes the new problems arising from the impact of "multi-ethnic" on the national structure under the background of globalization, which highlights the basic significance of the national mechanism to the modern country. it also discusses the deep problems about strengthening the national construction. Based on the historical investigation of the transformation from the traditional state to the modern state and the construction and operation of the modern state, this paper reveals the basic significance of the nationalization and integration of the population contained in the nation to the modern state. thus, it makes a new explanation to the operating mechanism, national ethics and evolution law of the modern state, and effectively expands our country's political cognition of the nation-state and the nation.