During the past three years, a revolutionized radical surgical approach for rectal cancer ("down to up TME " approach or "transanal TME (TaTME)"approach, which is opposite to the conventional approach) has emerged and it is a concept that combines natural orifice transluminal endoscopic surgery(NOTES) and total mesorectal excision(TME) with curative intent. The feasibility, safety and reproducibility of it were first demonstrated in swine survival experiments and subsequently in human cadaver series, and then it was successfully applied to human patients in few centers around the world, most of which were performed with assistance of laparoscopy, namely hybrid transanal TME. In addition, pure-NOTES without conventional laparoscopic assistance (no scar) has also been demonstrated, though the cases were more limited. In the initial stage, our group has successfully performed this no-scar transanal TME in a series of human cadavers with satisfactory outcome. Hence the investigators conduct this study, looking to see if this pure transanal NOTES investigational procedure is a safe and effective approach to radically remove rectal cancer of the mid and lower rectum and meanwhile, if it can reduce pain, gain faster recovery and better function and life quality when gaining the best cosmetic effect.