The rate of anastomotic leakage after laparoscopic anterior resection（LAR） for medium & low rectal cancer is still high. the transanal drainage tube (TDT) was thought to be useful for deduce the rate. There were several studies, but most of them were not randomized controlled trial (RCT) studies. There was only one RCT study with enough samples, but it was designed for open anterior resection, and the patients underwent diverting stoma were excluded, so there was the selection bias. LAR now is thought to been with the same effect, and it is safe and feasible. So a RCT investigation for the use of TDT for prevention of anastomotic leakage after LAR for medium & low rectal cancer is needed.