Abstract： Alzheimer's disease (AD) is a common neurodegenerative disease. In recent years， many studies have shown that dyshomeostasis of gut flora is closely related to the development of AD. Alzheimer's disease belongs to the dementia in Chinese medicine， featuring "tendency of phlegm is the most exuberant and degree of dementia is the deepest"，and pathogenic phlegm is the etiology of AD. By sorting out the correlation between gut flora， pathogenic phlegm and AD in terms of etiology and pathogenesis， the authors explain the similarities between gut flora disorders and the theory of diseases caused by pathogenic phlegm， and summarize the main treatment methods of fortifying the spleen， soothing the liver and resolving phlegm，tonifying the kidney and activating the blood to resolve phlegm， and warming yang to resolve phlegm. Finally the authors elaborate the characteristics of the prescriptions for treating phlegm， namely， Xixin Decoction and Ditan Decoction， and their curative effects， which provides a theoretical basis with modern scientific meaning for the treatment of AD from phlegm in Chinese medicine.