Abstract: The pursuit of community is the universal law of the development of human society, and the community of nation-state is the most important community form in the era of nation-state. The evolution of the nation-state community is not accomplished in one move, and it presents stage characteristics. The establishment of the nation state community endows the ethnic rights to be politically attached, making the national issue and the class issue become the most important subject of the community and the national issues are becoming more and more intense. As a community in the sense of culture, territory and politics, they are not always mono-nature doctrine or consistent, but complex. It is because of this complexity that the expansion of ethnic rights within the community can lead to ethnic crisis. However, the expansion of ethnic rights is not unlimited. It is always bound by certain boundaries, and there is a balance between the upper limit (the nation-state community refuses to secede) and the lower limit (the ethnic refuses to assimilate). National engineering is an important way and feasible choice for the governance of ethnic affairs to ensure that the impact of the expansion of ethnic rights on the boundary of community is controllable.