Four days of menstruation after hysteroscopic surgery falls within the range of normal menstrual period time. If there is a significant shortening from the preoperative period, it is considered to be related to the endometrium not yet repaired, endometrial damage, and uterine cavity adhesion. 1. The endometrium has not yet been repaired: Since the endometrium is often scraped during hysteroscopic surgery, some patients’ endometrium has not yet been fully repaired during menstruation, so they may experience low menstrual flow and shortened menstrual period, which usually lasts for 2~3 menstrual cycles and then the symptoms can be relieved on their own. 2. Damage to the endometrium: If the endometrium is damaged during diagnostic scraping, the endometrium basal layer may be damaged, resulting in the endometrium not being able to regenerate, so shortening of menstrual period may also occur. 3. Uterine adhesion: after hysteroscopic surgery, as the two layers of the endometrium are exposed to fresh trauma, so there is a possibility that the two layers will be adhered, so the shortening of menstruation will also occur. The 4 days of menstruation belongs to the range of normal menstrual period, if there is obvious shortening after hysteroscopy and before the operation, it is recommended to go to the gynecology department of regular hospitals, improve the ultrasound and other related examinations, and clarify the cause of the disease under the guidance of the doctor and active treatment.