The common causes of stomach pain during menstruation are categorized into physiological and pathological, physiological causes are usually primary dysmenorrhea, and pathological causes include pelvic inflammatory disease, endometriosis and so on. 1. Physiological causes: dysmenorrhea is usually primary dysmenorrhea. The cause of primary dysmenorrhea may be due to poor discharge of the endometrium and excessive uterine flexion. It is common during puberty and the pain is spasmodic. 2. Pathologic causes: (1) Pelvic inflammatory disease: pelvic inflammatory disease-induced stomach pain is mainly due to inflammatory infection, there is invasion of pathogens, which will stimulate the tissues to appear swelling, oozing, congestion, which may be further aggravated during menstruation, thus triggering dysmenorrhea. (2) Endometriosis: The typical manifestation of endometriosis is progressive worsening dysmenorrhea, which is related to active endometriosis foci. If the stomach pain during menstruation is more serious, it is recommended to go to the hospital, identify the cause under the guidance of the doctor, and treat the cause.