Abstract: The discourse of“Children & Adolescent's Physical Fitness”reflects people's viewpoints on children and adolescents' physical fitness under different social and historical backgrounds, and has distinct practical characteristics. Drawing on Foucault's discourse theory, this article analyzes the discourse construction of“Children & Adolescent's Physical Fitness”from the perspective of knowledge archaeological, and draws the conclusion: Since the founding of the People's Republic of China, the concepts of“physical fitness”and“medical sports”(early 1950 s),“physique”(from the late 1970 s to the early 1980 s),“exercise prescription"(in the late 1980 s),“health”(in the late 1990 s), and“physical health”(in the early 21 st century) have successively formed a“concept group”; at the same time, with the help of sports medicine, sports physiology, sports psychology and other disciplines, the discourse space of children's sports fitness theory has been gradually constructed. From the perspective of genealogy, this article points out that the current discourse statement of the“physical health”theory provides the guidance of children and adolescents' physical fitness activities: Through the development of targeted sports prescription to help children and adolescents to prevent and treat diseases, improve the system health, promote physical and mental health, and obtain healthy body. Based on the above analysis, this article puts forward the following suggestions to improve the discourse of“physical fitness”of children and adolescents in China:On the one hand, we should pay attention to the combination of natural knowledge and humanities knowledge to form a new theoretical statement of children and adolescents' physical fitness; on the other hand, it is necessary to strengthen the coordination of power operation in the government, society, schools and other fields, so as to guide children and adolescents in physical fitness activities.