Shanghan Lun, is based on "exogenous cold disease, " the change rules of a series of diseases such as superficies tightened by wind-cold and yang deficiency and internal cold, and the rules of treatment based on syndrome differentiation have had a profound impact on traditional Chinese medicine in later generations. Formulae with the name of "Sini" and its variations have the effect of treating deadly cold limbs in ,Shanghan Lun, for example,Sini, Decoction,Tongmai Sini, Decoction,Baitong, Decoction,Fuling Sini, Decoction,Sini Renshen, Decoction,Danggui Sini, Decoction, and ,Sini, Powder, etc. Their corresponding constitution characteristics, etiology and pathogenesis, changes in disease status, and clinical manifestations have certain commonalities. This paper discusses and analyzes the modifications of the "Sini" formulae, the rules of the formulae, and the principles of application based on the characteristics of yang deficiency constitution, their susceptibility to disease, and the evolutionary pattern of yin excessiveness due to yang deficiency pathogenesis. Our aim is to deepen the knowledge and understanding of the application of the "Sini" formulae from the perspective of yang deficiency constitution and to provide research ideas for the comprehensive study of "constitution-disease-syndrome differentiation" .