Objective:To explore the vascularity index of joints synovial quantitatively evaluate activity degree of rheumatoid arthritis(RA).Methods:From January to April 2022, 102 cases of RA patients in Henan Provincial People′s Hospital were conducted ultrasound examination of 28 joints including the bilateral metacarpophalangeal joints (1-5), 1st interphalangeal and proximal interphalangeal joints (2-5), wrist joints, elbow joints, shoulder joints and knee joints. Superb microvascular imaging (SMI) was used to visualize and calculate the vascularity index (VI) in the hyperplastic synovium. Summary Vascularity index (VIsum) was calculated by adding the VI of 28 joints. Standard vascularity index (VIstand) was obtained by dividing VIsum by the number of positive joints. The mean vascular index (VImean) was obtained by dividing the VIsum by 28, which is the number of joints examined. The disease activity score in 28 joints (DAS28) was calculated, including DAS28-CRP and DAS28-ESR. Serological results related to RA were collected. The correlation between VIsum, VIstand, VImean and the above data were analyzed respectively. DAS28-ESR and DAS28-CRP stages were used as the criteria, receiver operating curve (ROC) was used, to evaluate the diagnostic efficacy, sensitivity and specificity of VI parameters in assessing RA activity.Results:VIsum, VIstand and VImean were positively correlated with DAS28-ESR, DAS28-CRP, ESR and CRP. The r values of VIsum and DAS28-ESR, DAS28-CRP, ESR and CRP were 0.703, 0.728, 0.467 and 0.529, respectively. The r values of VIstand and DAS28-ESR, DAS28-CRP, ESR and CRP were 0.665, 0.705, 0.538 and 0.605, respectively. The r values of VImean and DAS28-ESR, DAS28-CRP, ESR and CRP were 0.677, 0.690, 0.441 and 0.501, respectively (all P<0.01). Using DAS28-ESR as grouping standard, the area of ROC curve(AUC) of VIsum, VIstand, and VImean were 0.815, 0.816 and 0.814, respectively. With the cut-off value of VIstand being 12.83, the specificity and sensitivity of VIstand diagnosis were 0.882 and 0.676, respectively. Using DAS28-CRP as grouping standard, the AUC of VIsum, VIstand, and VImean were 0.812, 0.878 and 0.811, respectively. With the cut-off value of VIstand being 13.97, the specificity and sensitivity of VIstand diagnosis were 0.997 and 0.710, respectively. Conclusions:Synovitis VI can objectively evaluate the degree of synovitis activity in patients with rheumatoid arthritis. Synovial VI has high diagnostic efficacy for the activity of RA patients.