The reason for the pain in the left side of the abdomen is that prostatitis, intestinal tumors, stones, etc., and gynecological inflammation can also be caused by women. 1. Prostatitis: men who have the symptom of left abdominal distension and back pain should be considered as the result of prostatitis, which is easy to involve the tissues of the lower back and abdomen, leading to the symptoms of lumbar pain, abdominal pain, perineal pain, back pain, and thigh pain, which can be diagnosed clearly by the examination of prostate fluids and the test of the four-cup test. 2. Intestinal tumor: including colon cancer and rectal cancer. Patients may have left abdominal pain, blood in stool, diarrhea, urgency (discomfort in lower abdomen, wanting to defecate, feeling of incomplete defecation after defecation), lumbar pain, etc. Colonoscopy, abdominal CT and other tests can be performed to make a clear diagnosis. 3. Urinary stones: patients may have pain in the lower back or lower abdomen, lateral abdomen, in addition to hematuria, urinary frequency, urinary urgency, urinary pain, urethral burning sensation, dysuria, etc. Ultrasound, abdominal CT and so on can help to confirm the diagnosis. 4. Gynecological inflammation: adnexitis, ovarian cysts, ovarian corpus luteum cysts, etc. can appear left lower abdominal pain, lumbago and other symptoms. Routine urinalysis and gynecological ultrasound can be used to assist in the diagnosis. Caused by the left lower abdominal pain waist pain may also have other reasons, need to pay attention to timely hospital visits, clear causes, targeted treatment.