Endometriosis is a disease caused by the implantation of functional endometrial tissue in areas outside the uterus, often referred to as endometriosis, and is a common hormone-dependent benign gynecological disease. The causes of endometriosis are not fully understood, but there are several etiological theories as follows: 1. Ectopic implantation theory: Women’s menstrual blood contains endometrial tissue, and when menstrual blood reflux occurs, endometrium can be brought to other parts of the body, such as ovaries and pelvis. Endometrial tissue cells adhere to the peritoneal surface and invade into the peritoneum, causing inflammatory cells to gather at the site of the implantation, neovascularization around the lesion, and proliferation of endometrial cells, resulting in the formation of endometriotic lesions. Congenital vaginal atresia, cervical stenosis, etc. can obstruct the discharge of menstrual blood, thus easily leading to menstrual blood reflux; multiple uterine surgical operations such as cesarean section, abortion, tubal lavage, etc. can easily bring the endometrium to other sites for direct implantation. In addition, the endometrium can also spread to distant sites through the lymphatic and venous systems, resulting in ectopic implantation. 2. Somatic epithelial metaplasia theory: Ovarian epithelium and pelvic peritoneum are differentiated from somatic epithelium. When these tissues are repeatedly stimulated by ovarian hormones, menstrual blood and chronic inflammation, they can be activated and transformed into endometrium-like tissue. Endocrine theory: endometriosis is a hormone-dependent disease that does not develop during puberty. The endometriosis foci can gradually atrophy and absorb after perimenopause and bilateral oophorectomy. Pregnancy or the use of sex hormones to suppress ovarian function can control disease progression. Therefore, it is believed that the occurrence and development of endometriosis are related to female hormone levels. 4. Induction theory: Undifferentiated peritoneal tissue can form endometrium-like tissue under certain endogenous biochemical induction. 5, angiogenesis theory: there are a large number of neovascularization on the surface of the lesion and surrounding tissues of endometriosis, and a large number of tissue growth factors are jointly involved in the formation of neovascularization, so it is believed that vascular endothelial growth factor is related to endometriosis. In addition, genetic factors, immune and inflammatory factors, etc. may also be related to the occurrence of endometriosis.