The large amount of blood clots on the second day of menstruation is considered to be caused by physiological factors as well as pathological factors, which are commonly found in ovarian tumors, uterine fibroids, endometrial polyps and so on. 1. Physiological factors: If the patient has his first or second menstrual period after giving birth to a child, or has had an abortion in the previous month, etc., when the menstrual period has just resumed, the amount of menstruation may also be increased, accompanied by blood clots, which belongs to a relatively normal physiological phenomenon. 2. Pathological factors: (1) Ovarian tumor: ovarian tumor may lead to excessive estrogen secretion, which may affect menstruation and lead to excessive menstrual flow, resulting in the phenomenon of blood clots. (2) Uterine fibroid: it is a common benign tumor of female genitalia, mainly caused by heredity, increased level of sex hormone, stem cell dysfunction, etc. It can lead to the emergence of uncomfortable symptoms such as increased menstruation and prolonged menstruation, and so it can also cause a large number of clots on the second day of the menstruation. (3) Endometrial polyps: mainly caused by high estrogen level and inflammation stimulation. The appearance of endometrial polyps can cause patients to have heavy menstrual flow, prolonged menstrual period and other abnormal manifestations. Therefore, when patients have a large number of blood clots on the second day of menstruation, they should go to the hospital in time to find out the cause and actively treat it.