1. To observe and measure the distance between the origin of LCA (left colonic artery，LCA) and IMA (inferior mesenteric artery，IMA) root and the distance between IMA and IMV (inferior mesenteric vein，IMV) at the origin of LCA in rectal cancer patients. Statistical analysis of intraoperative measured data, on the basis of the original anatomical relationship, to achieve anatomical localization of quantitative and accurate, for the preservation of LCA laparoscopic radical resection of rectal cancer to provide a strong anatomical basis. 2. The operation time, 253 lymph node dissection time, intraoperative blood loss, postoperative anal exhaust time, postoperative feeding time, postoperative hospital stay, postoperative ischemic colitis rate and postoperative anastomotic leakage rate of patients with laparoscopic radical resection of rectal cancer with preservation of LCA were recorded. The surgical efficacy and clinical significance of laparoscopic radical resection of rectal cancer with preservation of LCA were evaluated.