Standardized lymph node dissection and negative surgical margins are fundamental to achieving optimal outcomes in radical resection for colorectal cancer. However, discrepancies exist among international guidelines (e.g., European/American vs. Japanese) regarding the optimal extent of bowel resection, particularly the length of the distal margin in rectal cancer, which directly influences surgical approach and decisions on functional preservation. This article aims to systematically review the theoretical basis for the extent of intestinal resection in colon cancer and rectal cancer at different sites. By analyzing and comparing the Western concept of total mesenteric excision with Japanese data on precise measurements based on lymph node metastasis patterns, this paper focuses on the principles for resection margins: 10 cm for both proximal and distal margins in colon cancer, 3 cm for rectosigmoid and high rectal cancer, 2 cm for low rectal cancer, and special considerations (e.g., post-neoadjuvant therapy, poorly differentiated types). Key research data are summarized to provide evidence-based references for surgeons to develop individualized and precise surgical strategies in clinical practice.