Thickness of the endometrium is not necessarily cancerous, and is classified into physiological and pathologic. With the change of menstrual cycle, women’s endometrium will gradually become thicker. Secondly, it may also be caused by endometrial hyperplasia, endometrial cancer and other diseases. 1. Physiological factors: the endometrium of a woman will continue to thicken on the 15th day after menstruation under the influence of progesterone secreted by the ovary after ovulation, in order to prepare for the implantation of the fertilized egg. Thickness of the endometrium is considered a physiological phenomenon. 2. Endometrial hyperplasia: endometrial hyperplasia is a kind of non-physiological, non-invasive endometrial abnormality proliferation, which is mainly caused by long-term estrogen stimulation without progesterone antagonism, and endometrial thickening can be found in ultrasound examination. 3. Endometrial cancer: if endometrial cancer spreads and causes cancer cells to invade myometrium, it will lead to localized endometrial thickening. Patients may have symptoms such as abnormal vaginal discharge and irregular vaginal bleeding. There are various causes of endometrial thickening, and patients are advised to go to the hospital for relevant examinations to find out the causes of the disease.