Bowel preparation is closely llined to the quality of colonoscopy, inadequate bowel preparation (IBP) could lead to higher miss rate of adenomas, patients' discomfort and higher health expense. For the patients with possible IBP before the examination, it may be better to cancel the colonoscopy and repeat bowel preparation through modified or enhanced strategies. Thus, it is important to set up a model to predict the quality of bowel preparation individually.

Inclusion Criteria:

• Patients aged 18-90 years old who undergoing colonoscopy

Exclusion Criteria:

• failed colonoscopy because of technical chanllenge or poor tolerance of patients
• history of colorectal surgery
• prior finding of severe colonic stricture or obstructing tumor
• dysphagia
• compromised swallowing reflex or mental status
• significant gastroparesis or gastric outlet obstruction or ileum
• known or suspected bowel obstruction or perforation
• pregnancy
• unable to give informed consent

This is a prospective study involving two tertiary-centers in China.