The surgical management of ultra-low rectal cancer faces a challenging balance between oncological radicality and functional preservation. This review focuses on the bottleneck of functional sphincter preservation for ultra-low rectal cancer, systematically elaborates the theoretical basis and clinical value of irregular (conformal) distal-margin resection, and proposes this approach as the core strategy for functional sphincter preservation. This approach employs personalized and conformal precision excision to maximize the preservation of intestinal tissue and sphincter muscles while ensuring oncological radicality, thereby significantly improving postoperative anal function. With advances in neoadjuvant therapy, immunotherapy, and surgical techniques, this strategy provides a framework for balancing radical tumor control and functional preservation in patients with ultra-low rectal cancer. The evolution of this concept is expected to pave a way for future sphincter-preserving surgery.