Introduction: Previous studies, using clinical trial data, demonstrated that once-weekly (OW) semaglutide is dominant versus other glucagon-like peptide 1 receptor agonists (GLP-1 RAs) in China. This study aims to evaluate the long-term clinical and economic effects of switching to OW semaglutide from other GLP-1 RAs among patients with type 2 diabetes mellitus (T2DM) in China. Methods: The Institute of Health Economics Diabetes Cohort Model (IHE-DCM) was used to project life expectancy, quality-adjusted life years (QALYs), and total direct medical cost over 40 years from a Chinese healthcare system perspective. Baseline characteristics, clinical effectiveness, and the treatment dose of OW semaglutide were derived from previously real-world studies. Patients were assumed to switch to semaglutide or continue previous GLP-1 RAs for 3 years and change to intensive therapy. Drug prices were based on the median bidding price in January 2024 in China. Costs of other GLP-1 RAs were calculated on the basis of their market share in China. All costs were accounted as 2023 Chinese yuan (CNY). A discount of 5% was applied. One-way sensitivity analyses and probabilistic sensitivity analyses were used to test the robustness of the base-case result. Results: The results show that switching to OW semaglutide from other GLP-1 RAs among patients with T2DM in China can improve life expectancy by 0.02 years and afford an additional 0.12 QALYs per patient. Meanwhile, switching to OW semaglutide is associated with decreased total lifetime direct medical costs of 4204 CNY per patient, mainly resulting from savings in microvascular costs (2214 CNY) and macrovascular costs (1228 CNY). Sensitivity analyses show the robustness of modeling projection findings. Conclusion: Based on real-world data from China, this modeling projection study demonstrates that switching to OW semaglutide from other GLP-1 RAs can have better clinical and economic effects for patients with T2DM in China, indicating it as a dominant treatment choice.