In the diagnosis and differential diagnosis of constipation, the necessary tests should be done according to clinical needs. First of all, attention should be paid to the presence of alarm symptoms and evidence of the presence of other organic lesions in the body; colonoscopy should be performed to exclude the possibility of colorectal tumors in patients over 50 years old with a history of long-term constipation and worsening symptoms in a short period of time; for long-term laxative abuse, colonoscopy can determine the presence of catharticcolon or (and) colonic melanosis; barium enema angiography helps in the diagnosis of congenital megacolon. If OOC is suspected, anal examinations and fecal imaging are necessary. Special tests include: gastrointestinaltransittest (GITT), rectal and anal manometry (RM), recto-anal reflex test, and many more tests, which are chosen only in cases of refractory constipation. The following tests are commonly used for refractory constipation: 1.Fecal routine and occult blood, which should be routine tests. 2, anorectal finger examination, which can understand the presence of masses and the function of the anal sphincter. 3, colonoscopy or barium enema helps to determine the presence of organic etiology. Especially when there is a recent change in stool habit, blood in the stool or other alarm symptoms (such as weight loss, fever), whole colon examination is recommended to clarify the presence of organic lesions such as colon cancer, inflammatory bowel disease, colon stricture, etc. 4.Gastrointestinal transmission test (GITT) is helpful to determine the presence of slow transmission, and is often taken at 48h and 72h. 5.Fecal imaging can dynamically observe anatomical and functional changes in the anorectum. Defecography can assess the speed and completeness of rectal emptying, the degree of anorectal angle and perineal descent. In addition, fecal imaging can detect organic lesions such as huge rectal protrusion, rectal mucosal prolapse or overlap. 6.Anorectal manometry can check the anorectal function for any obstruction. 7.Other patients with obvious anxiety and depression should be investigated and the causal relationship with constipation should be judged.