Colonoscopy is widely considered as the main choice for patients with suspected colorectal disease,and for screening those at high risk of colorectal cancer. However， colonoscope examination,especially those unsedated ones for screening,may bring much pain to patients,even induce some severe complications such as perforation.Considering the increasing need of colonoscopy examination for screening purpose,it has been a problem deserving of further study that how to reduce pain and ensure safety during the procedure.Some studies suggest that use of Magnetic endoscopic imaging(MEI) during colonoscopy has the potential to ease patient discomfort and reduce complications.Theoretically,the MEI could accurately depict the position of the scope in three dimensions and help avoid forcefully feeding the colonoscope through loops of vulnerable bowel,thus alleviating patient pain and promoting procedure safety.However,the problem whether MEI system could help reduce patient pain during procedure effectively，especially in inexperienced colonoscopists，still remains controversial for researchers,and no study has been designed to test the hypothesis that MEI may help decrease the risk of some complications,such as colon perforation.In this study we aim to evaluate the he efficacy of magnetic scope navigation on patient pain during unsedated colonoscopy；In addition，we try to construct a simple colon force measurement device ,and by using this device to observe the variation of force exerted on colon loop ,we expect to find the potential mechanism of pain-alleviation and explore the possible effect of complication reduction during colonoscopy under the influence of MEI system.