Abstract: Based on the detailed description of the origin， development and maturity of "Eight Principles"， this paper pointed that ignoring the logic defects on equally treating the importance of "Eight Principles" yin， yang， exterior， interior， cold， heat， deficiency and excess syndromes would lead to students' confused understanding of the concept of "yin and yang syndrome differentiation" as well as its connotation. It is suggested that the recapitulative and governing status of yin and yang should be emphasized. That is to say， "Two Principles" and "Six Essentials" should be discussed respectively under the chapter named "Eight Principles Syndrome Differentiation" so as to ensure the completeness of "Eight Principles"， stress the recapitulative and governing status of yin and yang， and fully reflect the hierarchy of "Two Principles" and "Six Essentials".