The work aims to focus on crotch trousers, a special type of women??s daily wearing emerging in the Southern Song Dynasty, to clarify its developmental course and historical place in the costume culture of the Song Dynasty and China. Based on the “Painting of Auguries of Revival”, the emergence, fashion and popularity of crotch trousers are examined combined with images, literature and physical artifacts to explore the spreading and evolving characteristics of crotch trousers in different social classes of women through different period in the Southern Song Dynasty. The cultural value of crotch trousers is revealed from the perspective of tailoring technology, and the driving force for the popularity of crotch trousers in the era is explored in three aspects-social environment, women??s rights and interests, and fashion. The historical emergence of crotch trousers is a symbol of quantal leap from underwear to outerwear for the upper class women of Han nationality, which has broken the away from the long tradition of emulating and adapting men??s clothing elements and created a new paradigm of women??s clothing ingeniously, becoming popular in the Southern Song Dynasty for more than 100 years and achieving remarkable significance in the history of Chinese trousers.