The anatomic variation of the inferior mesenteric artery system has important clinical significance in rectal cancer radical operation.The variation required a thorough lymph nodes cleaning from the inferior mesenteric artery to the root of the left colic artery root of central group of lymph node and preservation of the left colonic artery at the same time when dealing with the inferior mesenteric artery.It will not only reach the target of radical left colic artery, but also control the risk of operation, promote recovery after operation, and reduce the postoperative complications such as anastomotic fistula et al.The understanding of the anatomic variation of the sigmoid colon and inferior mesenteric vein suggests the cautiousness in operation and prevent the complications such as accidental bleeding et al.