The endometrium thickens and sheds during each physiological cycle in response to hormonal changes in the body to form menstruation. Endometrial thickening is the thickening of the lining of the uterus beyond normal thickness due to excessive proliferation of the endometrium. It is important to first clarify the cause of endometrial thickening. If the endometrial lining is temporarily overgrown due to hormonal instability in the body, and the overgrown lining will be completely shed during the next or next few menstrual cycles after the body’s endocrine disorder is adjusted, this situation will not be harmful. However, if the thickness of the endometrium exceeds normal for a long time, menstrual disorders may occur, with various forms of irregular uterine bleeding, with periods of varying length, bleeding in large amounts at times, or even in large amounts without regularity, and if the bleeding is prolonged, it may cause anemia or infection. Women of reproductive age, especially those with combined anovulatory uterine bleeding, can cause infertility. In addition, we should be alert to endometrial thickening caused by pathological factors, such as the possibility of endometrial polyps, endometrial atypical hyperplasia (precancerous lesions) or even endometrial cancer. Endometrial cancer is one of the three common malignant tumors of female genitalia, which can seriously affect women’s health. For the phenomenon of endometrial thickening, it is most important to clarify its etiology.