The endometrium thickens and sheds during each physiological cycle in response to the changes in estrogen and progesterone secreted by the ovaries in the body to form menstruation. During the follicular phase, the epithelium and mesenchyme of the endometrium show proliferation under the action of estrogen, and during the luteal phase, the endometrium shows a secretory response under the action of progesterone, which is called the secretory phase. The thickness of the endometrium changes continuously during a menstrual cycle. Endometrial thinness refers to the failure of the endometrium to reach a thickness of 8 mm when the follicles are mature (mid-menstruation), which may affect the menstrual flow and the fertilization of the egg, causing infertility or early miscarriage. The causes of this condition may include: low estrogen and progesterone levels due to gynecological endocrine disorders; damage to the endometrium and adhesions after multiple medical abortions, multiple abortion cleanings, curettage, or electrosurgery; chronic inflammation of the endometrium; and, rarely, malformations of the uterus. To treat endometrial thinning, it is important to check the level of sex hormones at the same time to determine the cause, because the treatment for endometrial thinning caused by different factors is different, so targeted and individualized treatment should be given.