This is a prospective, randomized, double-blind controlled trial. Elderly patients with constipation requiring colonoscopy were randomly divided into four groups: 1. Received both gastrointestinal external stimulation and transcutaneouselectrical acupoint stimulation; 2. Received gastrointestinal external stimulation singly; 3. Received transcutaneouselectrical acupoint stimulation singly; 4. No stimulation was given. All groups received oral administration of polyethylene glycol for intestinal cleansing. Boston Bowel Preparation Scale (BBPS) score was used to assess the quality of intestinal cleanliness , with a total score of 9, and higher scores indicating better intestinal cleanliness, and BBPS≥6 was defined effective.

The early detection of intestinal lesions is extremely important, and the quality of intestine cleanliness is an important factor for the quality of colonoscopy. The elderly are at high risk of intestinal diseases. However, surveys have found that the overall quality of bowel cleanliness in elderly patients undergoing colonoscopy is poor, which affects the detection rate of colon lesions. This is a prospective, randomized, double-blind, controlled clinical trial to observe whether combined gastrointestinal surface stimulation and transcutaneous electrical acupoint stimulation can improve the quality of bowel cleansing and increase the detection rate of intestinal diseases. Elderly patients with constipation requiring colonoscopy were randomly divided into four groups: 1. Received both gastrointestinal external stimulation and transcutaneouselectrical acupoint stimulation; 2. Received gastrointestinal external stimulation singly; 3. Received transcutaneouselectrical acupoint stimulation singly; 4. No stimulation was given. All groups received oral administration of polyethylene glycol for intestinal cleansing. Boston Bowel Preparation Scale (BBPS) score was used to assess the quality of intestinal cleanliness , with a total score of 9, and higher scores indicating better intestinal cleanliness, and BBPS≥6 was defined effective.

Inclusion Criteria:

1. Age 60-80 years old;
2. Colonoscopy was planned;
3. The diagnosis of constipation was in accordance with Rome Ⅳ criteria.

Exclusion Criteria:

1. Acute myocardial infarction (within 6 months), severe heart failure (New York Heart Association class II-V, chronic renal failure (CKD stage II-V), or mental disorder;
2. Colorectal resection;
3. Drugs of aspirin, warfarin, or other anticoagulants, and coagulopathy;
4. Oral administration any drugs that may affect gastrointestinal motility, such as proton pump inhibitors, non-steroidal anti-inflammatory drugs or antibiotics (within 4 weeks), probiotics (within 2 weeks);
5. The following diseases：inflammatory bowel disease, frequent diarrhea, severe gastroparesis, intestinal perforation or obstruction;
6. Participating in other clinical trials.

The Participants, investigators and outcomes Assessor don't know receiverd which intervention, only care Providers know it.