Objective: To evaluate the clinical efficacy of blood-letting cupping combined with manual lymphatic drainage in treating breast cancer-related lymphedema (BCRL) and explore its mechanism of action from both traditional Chinese medicine and modern medical perspectives, providing a scientific basis and novel therapeutic approaches for clinical management of BCRL. Methods: Patients with BCRL admitted to the outpatient and inpatient departments of Hebei University Affiliated Hospital were enrolled. A prospective randomized controlled trial design was adopted, with eligible patients randomly assigned to a treatment group and a control group. The control group received manual lymphatic drainage alone, while the treatment group received manual lymphatic drainage combined with blood-letting cupping therapy. Post-treatment comparisons evaluated upper limb circumference reduction, edema severity grading, and upper limb functional scores. Vital signs and adverse reactions during treatment were recorded for both groups. Statistical software analyzed the data. Results: The treatment group demonstrated significantly greater reduction in upper limb circumference, improvement in edema severity, and higher upper limb function scores compared to the control group (P < 0.05). Vital signs remained stable throughout treatment in both groups. No severe adverse reactions occurred in the treatment group; only isolated cases of mild skin itching were reported, which resolved after symptomatic management. Conclusion: The combination of blood-letting cupping and manual lymphatic drainage demonstrates reliable efficacy in treating BCRL, effectively alleviating edema symptoms and improving upper limb function with high safety. Its mechanism may relate to traditional Chinese medicine principles of “unblocking meridians, promoting blood circulation, and resolving stasis” and modern medical concepts of “enhancing local blood circulation, facilitating lymphatic drainage, and reducing inflammatory responses”.