Objective: The paper evaluates the effect of centralized medical consumables procurement policy on expenses of patients undergoing knee arthroplasty and analyzes the law of cost change, providing evidence for reasonably controlling the cost of these surgeries. Methods: Based on the real-world data before and after the implementation of policy, RDD was applied to analyze the impact of centralized medical consumables procurement on the hospitalization costs of patients undergoing knee arthroplasty. Results: After the implementation of centralized medical consumables procurement policy, the hospitalization costs of patients undergoing knee arthroplasty have significantly decreased. The optimal bandwidth was approximately 57.48 days, and the average hospital expenses of patients decreased by 23311.29 yuan on April 30, 2022. The estimated results of 1/2 optimal bandwidth showed that the expenses decreased by 24923.05 yuan, and the estimated results of 2 times optimal bandwidth showed that the expenses decreased by 21547.30 yuan. The local average effect of different bandwidths is slightly different, but all shows a decreasing trend. Conclusion: The centralized medical consumables procurement policy has effectively reduced the hospital expenses of patients undergoing knee arthroplasty. Hospital managers should strictly implement the procurement policy, improve clinical pathways and standardize diagnosis and treatment behavior to reduce patients’ expenses. In addition, relevant departments should steadily expand the scope of procurement and strengthen supervision to ensure the effective implementation of policy and improve the accessibility and affordability of medical services.