Understanding about the method of treatment of Sini San nowadays is for relieving liver qi stagnation. Sini San is also the basis of Xiaoyaosan, Chai Hu Shu Gan Tong . Opinions about its etiology and pathogenesis in Shanghan Zabing Lun, are still widely divided. In this article, we beased on Shanghan Zabing Lun and discussed by the traditional Chinese medicine theory from Huangdi Neijing and The Explanation of Sheng Nong's Herbal Classic, to realize the medical mechanism and pathogenesis of Sini San in Shanghan Lun.