Lower abdominal distension is considered to be related to diseases of the intestinal system, urinary system and reproductive system. 1. Intestinal system: intestinal diseases, such as benign and malignant tumors of the intestinal tract, enteritis caused by various pathogenic bacterial infections, ulcerative colitis, etc., will affect the intestinal function, resulting in lower abdominal distension and pain, and some patients will be accompanied by changes in bowel habit or character. 2. Urinary system: diseases of the urinary system, such as inflammation, stones, tumors, etc., can cause lower abdominal distension, pain, patients may be accompanied by urinary symptoms, such as visible hematuria, urinary frequency, urinary urgency, urinary pain and other symptoms. 3. Reproductive system: women’s abdominal distension and pain are considered to be related to endometritis, ovaritis, pelvic inflammatory disease, pelvic effusion, tubal effusion, ectopic pregnancy and other factors. In addition to this, ovulation, menstruation, may also appear symptoms of abdominal distension. In men, small abdominal distension can also be considered to be related to prostatitis, varicocele and other diseases. To sum up, there are more causes of lower abdominal distension and pain, and it is recommended to go to the general internal medicine department, male department and gynecology department of the hospital for relevant examinations to clarify the causes.