Inclusion Criteria:  Patients are younger than 40 and over the age of 18. Clearly diagnosed with CSD. Experiencing clinical features of abnormal uterine bleeding, prolonged menstrual flow (the duration of menstruation is more than 10 days). The thickness of the remaining muscular layer of CSD was less than 3 mm. Normal range of blood sugar and insulin No serious medical problems (important viscera function in the normal range). No uterine fibroids, endometriosis, adenomyosis No malignant tumors. Sign the informed consent.  Exclusion Criteria:  Over the age of 40 or younger than 18; Indefinite diagnosis. Malignant tumors. With severe medical problems (severe liver disease, kidney disease, respiratory diseases, heart disease or uncontrolled diabetes, epilepsy, etc., dysfunction of important organs). Contraindications to metformin (baseline creatinine >124μmol/L, hypersensitivity to metformin, or a metabolic acidosis), use of drugs that might interact with metformin (glyburide, furosemide, or cationic drugs) Pregnant. Mental diseases. Unwilling to comply with the research plan.