On the basis of in-depth examination of the different types of multinational/ethnic states in the world,this article systematically analyzes the national and ethnic composition in different types of multi-national/ethnic states,and further uses the social identity theory to discuss the construction of national identity of various national and ethnic groups in different types of multi-national/ethnic states.The article argues:First,the multi-national/ethnic states in today’s world can be roughly divided into three types in which the first type is that the central(federal)government and local people both admit that there are several domestic"nations",the second type is that both the central(federal)government and local people admit that there is no domestic multiple"nations,"and the third type is that disagreements between the central(federal)government and local civilians in the existence of multiple domestic"nations."Second,the national/ethnic composition of the three different types of multi-national/ethnic states presents different complexities.Third within the first type o