The endometrium is not the wall of the uterus. The normal anatomical relationship of the uterus is as follows: the outermost layer next to the pelvic cavity is the plasma membrane of the uterus, inside the plasma membrane is the myometrium, inside the myometrium is the uterine cavity, and inside the cavity is the endometrium, which is the normal anatomical relationship of the uterus. If the endometrium changes, it will affect menstruation, such as thin endometrium, or thickened endometrium, or endometrial lesions, such as endometrial polyps, endometrial cancer, may cause abnormal menstruation in the clinical situation. Therefore, once clinical changes in menstruation are detected, it is important to observe the condition of the endometrium and give appropriate treatment if necessary.