The work aims to demonstrate the design motivation and mechanism of uniforms in primary and secondary schools from the perspective of semiotics. Through literature research, case analysis, in-depth interview and grounded theory, the three main categories of uniform design in primary and secondary schools are demonstrated with the "design motivation and mechanism" as the core coding. Among them, "functional attribute" and "emotional motivation" are juxtaposed, and the relationship between them and "design form" is causal. The three main categories jointly generate the theoretical framework of "design motivation and mechanism of uniforms in primary and secondary schools". The design mechanism of uniforms for primary and secondary schools is a symbol system jointly determined by "functional attributes" and "emotional motivation". In addition to the role of showing the image of the campus, enhancing the sense of belonging of students, and the sense of ceremony, it also bears the significance of campus management and order supervision, safety and protection as well as education. This is determined by the growth characteristics of teenagers. It is a symbolic utility system that must take priority over other needs.