Endometriosis (EM) is one of the most common diseases which severely affect the health and reproductive function for women of childbearing age. Though the basic and clinical research in past decades, we have formed our unique and systemic opinion about the etiology of EM. The abnormal endometrial tissue in EM patients flows backward to abdominal and pelvic cavity, completes three-step procedure of attachment- aggression-angiogenesis, and ultimately develops into EM. In all variable influencing factors, including immune, inflammation or local micro-enviroment, the character of eutopic endometrium determines the fate of the backward-flowing endometrial tissue, live or die; for women, being ill or not. By further deeply exploring, the stem cell or its micro-enviroment in eutopic endometrium might play the key role. Besides, EM is considered as a tumor-like disorder. Our series of conceptions about EM pathogenesis could be summarized as "3A"  model, "eutopic endometrial determinant"  theory, and "stem cell origination"  hypothesis. All in all, the study about development mechanism of EM ultimately will help to find out the more efficient and sensitive method for diagnosis, and exploit much effective measure of treatment as well.