Objective: To observe the clinical effect of modified Major Bupleurum Decoction in treating elderly patients with type 2 diabetes mellitus (T2DM) complicated by constipation, particularly its role in alleviating constipation symptoms. Methods: A clinical study was conducted on 60 elderly patients with T2DM complicated by constipation who were hospitalized in the geriatrics department of our hospital from January 2024 to December 2025. The patients were divided into groups based on the order of their visits. The control group (n = 30) received Western medicine treatment, while the treatment group (n = 30) received a combination of Western medicine and modified Major Bupleurum Decoction. Differences in traditional Chinese medicine (TCM) syndrome scores, constipation scale scores, glycemic and lipid metabolism indicators, treatment efficacy, and the incidence of adverse reactions were compared between the two groups before and after treatment. Results: Compared with the control group, the treatment group showed a significant reduction in TCM syndrome scores and CCS scores after treatment, along with an increase in treatment efficacy, with statistically significant differences (p < 0.05). Compared with the control group, the treatment group also demonstrated a significant reduction in glycemic and lipid metabolism indicators after treatment, with statistically significant differences (p < 0.05). Conclusion: Modified Major Bupleurum Decoction can actively improve constipation symptoms in elderly patients with T2DM complicated by constipation, with a definite therapeutic effect. Additionally, it exerts a certain auxiliary regulatory effect on the glycemic and lipid metabolism health of patients.