When the endometrial glands and mesenchyme invade the myometrium, it is called adenomyosis. The invaded endometrium is active and will bleed periodically like menstruation, thus making the cells of the myometrium grow larger and larger, causing diffuse enlargement of the uterus or the formation of globular nodules, leading to dysmenorrhea and abnormal menstruation, which is a benign disease. Why does the endometrium invade the myometrium? The etiology is not clear. Serial sectioning of adenomyosis specimens has revealed that some of the endometrial lesions in the myometrium are directly connected to the endometrium on the uterine cavity surface, so it is generally believed that the occurrence of this phenomenon is related to damage to the uterine wall during multiple pregnancies and deliveries, multiple abortions, and damage to the endometrial basal layer from chronic endometritis. In addition, because this disease is often combined with fibroids and hyperplasia of the endometrium, it is suggested that high levels of estrogen stimulation can also lead to invasion of the basal endometrium into the myometrium. To address the above causes, women can do the corresponding prevention work in their daily life, safe contraception, reduce abortion, do the prevention of reproductive tract infection, avoid strenuous activities during menstruation, and prohibit sexual intercourse.