There are many reasons for perianal swelling and pain: first, the more common is perianal abscess, after the anal gland infection spreads along the anal canal or rectum, thus leading to pus around the anus, with obvious fluctuations, which usually causes discomfort and swelling around the anus, thus causing swelling and pain, and perianal ultrasound can make a clear diagnosis. Secondly, if there is stool retention, long-term constipation makes the lower rectum suck the water dry, thus leading to obstruction of stool discharge, which will also lead to perianal distension and pain. If the skin of the anal canal is fractured due to fecal irritation and local co-infection, it will also lead to perianal distension and pain during feces, which can be diagnosed by visual examination, rectal diagnosis and, if necessary, anoscopy. There are many causes of perianal swelling and pain, so we should ask whether there is a history of trauma or foreign body invasion, combine with clinical examination to clarify the cause, and then treat the symptoms.