The main causes of pain in the left lower abdomen when pressed are, digestive system diseases, gynecological diseases, urinary tract diseases, etc.. 1. Digestive system: such as ulcerative colitis, sigmoid colon obstruction, etc., intestinal obstruction is usually manifested as paroxysmal pain, at the same time, anal defecation and exhaust disappear, accompanied by vomiting, etc.; ulcerative colitis in addition to the pain in the left lower abdomen when pressed, there is mucus, pus and blood stools, fever, etc.; sigmoid colon cancer or rectal cancer can cause pain in the left lower abdomen when pressed, and at the same time there is also lethargy, blood in the stools, etc.. 2. Gynecological diseases: the common gynecological diseases that cause pressure pain in left lower abdomen include left adnexitis and tuberculosis; left tubal ectopic pregnancy, left adnexal tumor, etc. These diseases will cause pressure pain in left lower abdomen. 3. Urological diseases: left ureteral tuberculosis, tumors, etc. will also cause left lower abdomen pain on pressure. Therefore, there are more reasons that cause pain in the left lower abdomen when pressed, and patients with any discomfort should consult a doctor in time to get a clear diagnosis and early treatment so as not to delay the condition.