Objective To investigate the role of age in the effect of joint replacement surgery on degenerative osteoarthritis of the knee in elderly patients. Methods A total of 68 elderly patients with knee degenerative osteoarthritis who received joint replacement surgery from June 2019 to August 2022 were selected as study subjects, including 35 patients ≤ 70 years old as the observation group, and 33 patients >70 years old as the control group. After joint replacement surgery, the recovery of the two groups of patients was observed. Results The observation group's joint range of motion （ROM） score and knee joint function HSS score were higher than the control group's at 6 months after surgery （P<0.05）. The Barthel index and 36-item Short-Form （SF-36） score of the observation group patients at 6 months after surgery were higher than those of the control group （P<0.05）. The incidence of complications in the observation group was lower than that in the control group （P<0.05）. The excellent and good rehabilitation rate of the observation group patients was higher than that of the control group （P<0.05）. Conclusion In the clinical treatment of elderly patients with degenerative osteoarthritis of knee joint, joint replacement surgery can effectively alleviate the pain symptoms and promote the recovery of their knee joint function. The choice of the timing of joint replacement surgery will affect the curative effect to some extent. Patients younger than 70 years of age have better functional recovery after joint replacement surgery than patients older than 70 years of age.