The treatment of polycystic ovary syndrome(PCOS) can be guided by the membrane source theory.With the disease location belonging to membrane source in narrow sense and the disease nature of deficiency-excess in complexity,PCOS has the characteristics of membrane source disease:long course,easy to recur and difficult to cure.The pathogenesis of PCOS lies in insufficient kidney qi,liver depression and spleen deficiency,leading to imbalance of qi and liquid and phlegm generation.Phlegm-dampness is not only the cause of PCOS,but also the important pathological product,which can be regard as a starting point for the treatment.From the perspective of the membrane source theory,the treatment of PCOS should focus on tonifying spleen,replenishing kidney,regulating qi,opening onto pleurodiaphragmatic interspace,drying dampness and resolving phlegm.For PCOS patients with the clinical characteristics of obesity and syndrome of phlegm-dampness block,Dayuan Decoction would be a beneficial therapy.This study discussed PCOS based on the membrane source theory,aiming to explore a new way of clinical diagnosis and treatment of PCOS,enrich the scientific connotation of membrane source theory and facilitate the modern clinical application of the unique theory of traditional Chinese medicine.