Under normal circumstances, the endometrium covers the surface of the uterine body cavity. If, due to some factors, the endometrium grows in other parts of the body, it can become endometriosis. This ectopic endometrium not only has endometrial glands in histology, but is also surrounded by endometrial stroma; in terms of function, it changes significantly with the estrogen level, that is, it changes with the menstrual cycle, but only part of it is affected by progesterone, and can produce a small amount of menstruation and cause various clinical phenomena. If the patient becomes pregnant, the ectopic endometrium may have decidual changes. Although this ectopic endometrium grows in other tissues or organs, it is different from the infiltration of malignant tumors. The peak of this disease is between 30 and 40 years old. The actual incidence of endometriosis is far more than what is seen clinically. If a laparotomy is performed for other gynecological diseases and a careful pathological examination of the removed uterine appendage specimens is performed, it can be found that about 20% to 25% of patients have ectopic endometrium.