Objective To evaluate the therapeutic effects of diosmin and hydrochlorothiazide combined with Yiqi Huayu Lishui Decoction on upper limb lymphedema following breast cancer surgery.Methods We selected 150 patients with upper limb lymphedema following breast cancer surgery who were treated at the Panzhihua Integrated Traditional and Western Medicine Hospital from January 2022 to December 2023. Using a random number table method, the patients were divided into a control group (75 patients) and an experimental group (75 patients). The control group received diosmin and hydrochlorothiazide, while the experimental group received these medications in combination with Yiqi Huayu Lishui Decoction. We compared the two groups in terms of treatment efficacy, Traditional Chinese Medicine (TCM) syndrome scores, mean arm circumference, circumference measurements at five sites on the affected limb, upper limb function [assessed by the Disabilities of the Arm, Shoulder, and Hand (DASH) score], self-perceived symptoms of lymphedema [evaluated using the Lymphedema Breast Cancer Questionnaire (LBCQ) score], pain severity [measured by the Visual Analogue Scale (VAS) ], and the excellent-to-good rate of shoulder joint mobility.Results The overall effective rate in the experimental group was higher than in the control group (P < 0.05). The differences in TCM syndrome scores regarding swelling, numbness, and localized fixed pain of the affected limb, tenderness on palpation, fatigue, shortness of breath with reluctance to speak, dizziness, pale complexion, and spontaneous sweating before and after treatment were all greater in the experimental group than in the control group (P < 0.05). The differences in the mean arm circumference and arm circumference measurements at wrist crease, 10 cm above the wrist crease, elbow crease, 10 cm above the elbow crease, and axillary crease before and after treatment were all greater in the experimental group than in the control group (P < 0.05). The differences in DASH scores, LBCQ scores, and VAS scores before and after treatment were higher in the experimental group than those in the control group (P < 0.05). The excellent-to-good rate of shoulder joint mobility was higher in the experimental group than that in the control group (P < 0.05).Conclusion The combination of diosmin and hydrochlorothiazide with Yiqi Huayu Lishui Decoction can improve TCM syndromes, upper limb function, lymphedema symptoms, pain levels, and shoulder joint mobility in patients with upper limb lymphedema following breast cancer surgery, demonstrating favorable clinical efficacy.