Objective To compare the oncological and functional outcomes between preserving the left colic artery （LCA） and high ligation of the inferior mesenteric artery （IMA） during laparoscopic D3 lymph node dissection for rectal cancer. Methods A total of 162 patients with rectal cancer who received surgical treatment in our hospital from July 2021 to February 2024 were selected. These patients were randomly assigned by computer randomization to the low-position group （preservation of the left colic artery （LCA） with low-position ligation combined with D3 lymph node dissection） and the high-position group（adopted the dassic total mesovectal excision for rectal cancer， and the inferior mesenteric artery was ligated at a high level）， with 81 cases in each group. Surgical parameters， postoperative complications， tumor markers， and postoperative survival were compared between the two groups. Results The low-position group exhibited a longer operative time and a longer duration for lymph node dissection at the IMA root when compared to the high-position group （P < 0.05）. However， it required splenic flexure mobilization less frequently （P < 0.05）. Postoperatively， the serum levels of carcinoembryonic antigen （CEA）， carbohydrate antigen 19-9 （CA19-9）， and carbohydrate antigen 125 （CA125） decreased in both groups （P < 0.05）. In the postoperative period， both the low-position and high-position groups showed increases in LARS （low anterior resection syndrome） and residual urine volume （P < 0.05）， as well as decreases in single voided volume， maximum urinary flow rate， FSFI score， IIEF-5 score， resting anal pressure， and maximum anal sphincter pressure （P < 0.05）. The low-position group had lower LARS scores and residual urine volume than the high-position group （P < 0.05）， whereas the low-position group had higher resting anal pressure and maximum anal sphincter pressure than the high-position group （P < 0.05）. A comparative analysis between the two cohorts revealed that the incidence of anastomotic leakage was significantly lower in the low-position cohort than in the high-position cohort （P < 0.05）. During the 1-year follow-up， no deaths occurred in either group. The low-position group had 9 cases of local recurrence （11.11%） and 2 cases of distant metastasis （2.47%）， while the high-position group had 5 cases of local recurrence （6.17%） and 2 cases of distant metastasis （2.47%）. There was no statistically significant difference in progression-free survival between the two groups （P > 0.05）. Conclusion Under standardized D3 lymph node dissection， preserving the LCA yields oncological outcomes equivalent to those achieved by high IMA ligation. Meanwhile， it offers significant advantages in reducing the risk of anastomotic leakage and better preserving early postoperative defecation and urinary function.