Whether a 3-year-old child is megacolon can go to the hospital to do relevant imaging tests, anorectal manometry, take rectal tissue for pathological biopsy, rectal mucosal acetylcholinesterase histochemistry to diagnose whether a 3-year-old child is congenital megacolon. 1. Imaging examination: X-ray can be used to give the child a flat film of the abdomen and barium enema contrast examination, direct observation of each part of the intestinal lumen whether there is enlargement or distal primary stenosis. 2. Anorectal manometry: If the child has bloating, constipation and other symptoms of megacolon, you can put the pressure measuring instrument into the rectum, so that the contraction and relaxation, to check the internal and external sphincter, rectum and other functions and coordination of the patient with megacolon, rectal sensory capacity, maximum capacity and compliance can be significantly increased. 3. Pathological biopsy: Pathological biopsy can be performed on the patient’s rectal tissues to see if there are abnormalities such as ganglion cell defects, which is a reliable criterion for the diagnosis of the disease. 4. Histochemical examination of rectal mucosa acetylcholinesterase: histochemical staining of the submucosa of the rectum in children with congenital megacolon shows strong positive staining for acetylcholinesterase; there are a large number of stained unmyelinated nerve fibers and a lack of ganglion cells. The examination and diagnosis of congenital megacolon in a 3-year-old child should be carried out by a specialist, and it is recommended to consult a doctor in time to avoid delayed treatment.