 The most challenge for the surgery of low rectal carcinoma was whether to perform low anterior resection LAR and preserve anal function improving the quality of life for patients, for which anastomotic leak is a great obstacle with about 5-10 incidence in reported literature. Up to now, kinds of surgical devices have been employed to reduce anastomotic leak rate after LAR. Most of these anastomotic devices could not resolve the problem of dog ear phenomena. In the present clinical trial, the investigators use a double purse-string rectal anastomosis with KOL staple in laparoscopic anterior rectal resection for low or ultra-low rectal carcinoma, which will resolve the problem of dog ear. The investigators aim to demonstrate the safety, effectiveness of this procedure and establish a standard method for laparoscopic ultra-low anterior rectal resection. 