The pain in the left lower abdomen when menstruating is mainly due to the following clinical reasons: first, inflammation of the left adnexa, in itself with inflammation, the tissue will be congested and edematous, which will aggravate the state of pelvic congestion during menstruation, so there will be pain in the left lower abdomen, it is recommended to do a gynecological examination after menstruation is clean, basically to confirm the diagnosis, if there is inflammation, it is recommended to actively give Anti-inflammatory treatment is recommended. Secondly, because there is endometriosis lesion on the left side, clinically endometriosis lesion will also bleed during menstruation, so it will cause pain in the left lower abdomen. It is recommended to do ultrasound examination after menstruation to find out whether there is endometriosis lesion.