Objective To investigate the application of high frequency ultrasound in knee joint lesions of elderly patients with rheumatoid arthritis.Methods Fifty patients with rheumatoid arthritis were collected in Yangpu Hospital Affiliated to Tongji University from March 2015 to December 2016 as test group.Fifty healthy elderly people without knee joint lesion were randomly selected as control group.High frequency ultrasound was used to examine the patients in the test group and the Results of this examination were used to compare with those of the control group and observe four indexes: patellofemoral effusion,synovial thickness,cartilage thickness and blood flow in the lesion area.Results There was only a small amount of synovial fluid in the articular cavity in the control group,the thickness was (2.11± 0.94) mm,while the thickness of the test group was (10.33±2.74) mm,the difference was statistically significant (t=17.03,P<0.05);in the control group,there was no synovial hyperplasia,the thickness was (1.11±0.24) mm,while the thickness of the test group was (5.48±2.74) mm which was significantly higher than that of the control group (t=13.18,P<0.05);in the control group,the cartilage tissue was striated without echo band,the thickness was (1.76±0.29) mm,while the cartilage tissue of the experimental group had lesion,the thickness was (1.12±0.12) mm lower than that of the control group and the difference was statistically significant (t=6.44,P<0.05);in the control group,there was no blood flow signal in the joint cavity,while low-speed blood flow signal could be seen in the joint cavity of the test group,the difference was statistically significant (0 vs.96%,χ2=6.44,P<0.05).Conclusion High frequency ultrasonography is effective in the treatment of senile rheumatoid arthritis with high specificity,high sensitivity,low cost,high efficiency and simple operation and it is not subject to external conditions.Therefore,it is suitable for early examination of senile rheumatoid arthritis and clinical promotion.