Objective:To explore the application of ultrasound in the diagnosis and curative effect evaluation of knee joint diseases in elderly rheumatoid arthritis.Methods:From June 2018 to June 2019, 65 elderly rheumatoid arthritis patients with knee pain as the main complaint in the hospital were selected as the study group, and another 35 normal elderly people were selected as the control group. Ultrasound was used to observe and compare the classification of color blood flow in the knee joint, the classification of hydrops in the suprapatellar capsule and the classification of synovium thickness between the two groups. The patients in the study group received standardized treatment for 3 months, and the therapeutic effect of the patients in the study group was evaluated by ultrasound.Results:Among the 130 knee joints of 65 patients in the study group, 108 lesions were diagnosed by ultrasound, and the diagnostic rate was 83.08% (108/130). There were significant differences between the study group and the control group (P<0.05). There was significant difference in the thickness of suprapatellar capsule and synovium between the study group and the control group (P<0.05), but there was no significant difference in the thickness of intercondylar cartilage (P>0.05). After treatment, the epithelium fluid thickness and synovial membrane thickness of the study group patients were significantly thinner than before treatment, and the color blood flow signal was reduced (P<0.05), while the intersacral cartilage thickness was not significantly changed (P>0.05).After treatment in 65 patients in the study group, 45 patients experienced a marked improvement in their clinical pain symptoms, 13 patients were relieved, and 7 patients had no significant changes. 3 patients relapsed after stopping treatment and were controlled after retreatment.Conclusions:Ultrasound can diagnose knee joint lesions in elderly RA patients early, and can be used to evaluate the efficacy of knee joint lesions in elderly RA patients. It is worthy of clinical promotion.