Older adults are susceptible to intestinal tumors. Colonoscopy can screen colorectal cancer, adenoma and other diseases. There is a large demand for colonoscopy in the older adults, and the risk during peri-colonoscopy period is high. According to the common intestinal preparation methods and the characteristics of the older adults, the investigators propose a modified method, that is single administration of low dose polyethylene glycol (PEG). Specifically, take 30ml lactulose in the morning 1 day before the examination, and eat without residue in lunch and dinner, Take 2L PEG in the morning of the examination day and fast at breakfast and lunch of the day. Taking 4L PEG in 2 days as the control group. The fasting and diarrhea period is shorter in the modified group than that in the control group, and the dose of PEG is less. Lactulose, a laxative, is taken one day before the examination, and the intestinal preparation time is longer than that of single administration. The situation of comfort, sleep and fecal incontinence during the intestinal preparation of the two groups will be compared. The results of electrolyte, blood glucose and B-type brain natriuretic peptide between the two groups will be also compared. The effect of intestinal preparation will be evaluated by the standardization of Boston intestinal preparation scale, and endoscopist blind method will be used in colonoscopy.