To discuss pathological mechanisms of poly-cystic ovarian syndrome(PCOS) according to its clinical features. Methods: Based on the summary of past literature, elaborated the etiology and pathogenesis of PCOS. Results: System and accurate study on etiology and pathogenesis of PCOS is helpful to enhance the level of clinical diagnosis and treatment. Conclusion: Deficiency of kidney is the basic pathogenesis of PCOS, while liver depression, phlegm-damp, blood stasis are the main pathogenesis; however, during clinical practice, syndrome of intermingled deficiency and excess was the commonly seen clinical syndrome.