Colorectal cancer is the third most common cancer in men and the second most common cancer in women.There are about 14 million cases of colonoscopy in the United States every year. In recent years, the incidence of colorectal cancer in China has risen sharply, becoming a serious threat to people's health.For small(≤ 9mm) lesions, endoscopic biopsy forceps and cold snare polypectomy can be used to remove.For larger lesions, especially laterally spreading tumor,endoscopic mucosal resection is a classic method of treatment.With the increasing diameter of the lesion size(> 20mm),we also need to adopt endoscopic piecemeal mucosal resection or endoscopic submucosal dissection.

As IT, Hook knife, BB, and other devices appear constantly, foreign researchers recently adopted a variation of conventional EMR（CEMR）, namely endoscopic mucosal resection with circumferential precutting(EMR - P).The technology is superior to conventional EMR for 10 to 20 mm polyps.Moreover, preliminary studies suggest that it has good safety and efficacy, and may be a better method for treatment of 10-20mm polyps under colonoscopy.

This clinical trial is being conducted to compare the efficacy and safety of two methods of polypectomy, CEMR and EMR-P, for 10-20mm colorectal polyps.

Inclusion Criteria:

• One polyp or lesion of 10-20mm at the most proximal of colorectal
• Adult patients (≥18 years old)
• Polyps other than pedicled polyps

Exclusion Criteria:

• There was submucosal infiltration under endoscope
• Residual lesions after endoscopic resection
• Inflammatory bowel disease, familial polyps, electrolyte abnormalities, coagulation disorders, or severe organ failure
• Pregnant or nursing
• No informed consent has been signed
• Patients taking NSAIDs or other anticoagulants
• sedated colonoscopy