Colonoscopy is the gold standard in the diagnosis and treatment colorectal disease, but due to the uncomfortable or even painful procedure, a part of people unwilling to undergoing the examination and giving analgesic agents were recommended in several guidelines. However, use of analgesic agents have their own drawbacks, and nearly 70% patients felt no pain or only mild discomfort with the unsedated colonoscopy, routine administration of sedative or analgesic agents to all patients was considered as unnecessary. However, unsedated colonoscopy was thought to be an option for some but not for all, therefore a method to identify which patients at high risk for painful colonoscopy in preoperational stage is necessary.

Inclusion Criteria:

• aged 18-80 years
• underwent unsedated colonoscopy

Exclusion Criteria:

• no bowel preparation or colon cleansing by enema only
• no need to reach cecum
• prior finding of severe colon stenosis or obstructing tumor
• history of colectomy
• unstable hemodynamics
• pregnant
• unable to give informed consent.

The patients of the training cohort were enrolled form Xijing Hospital of Digestive Diseases. The patients of the validation cohort were enrolled from the Shaanxi Second People's Hospital.