Abstract： Objective:To explore the correlation between serological indicators related to rheumatoid arthritis（RA）and semi quantitative grading score by musculoskeletal ultrasound（MSUS）in coastal residents.Methods:A total of 100 patients with RA who were admitted to the Department of Rheumatology and Immunology of the First Hospital of Qinhuangdao from January 2022 to June 2023 were selected as the research objects. According to the Disease Activity Score of 28 joints（DAS28）scoring method，the patients were divided into four groups：high activity group，moderate activity group，low activity group，and remission group. The semi-quantitative grading score by MSUS was used to evaluate the wrist joints，the 2nd and 3rd metacarpophalangeal joints，the 2nd and 3rd proximal interphalangeal joints，and the 2nd and 5th metatarsophalangeal joints in each group. The levels of rheumatoid factor（RF），erythrocyte sedimentation rate（ESR），and C-reactive protein（CRP）were compared among the RA patients in each group. Pearson correlation analysis was used to analyze the correlation between semi quantitative grading score by MSUS and DAS28 score，RF，ESR，and CRP levels. Receiver operating characteristic（ROC）curve analysis was performed to evaluate the diagnostic value of semi-quantitative grading score by MSUS for RA.Results:As the condition aggravating，the DAS28 score of RA patients increased，and the levels of serum RF，ESR，and CRP showed a significant upward trend. Moreover，the scores of bone erosion，synovial hypertrophy，joint effusion，intra-articular synovial flow signal，and the total score were significantly reduced and lower in sequence from the high activity group，the moderate activity group，low activity group，to remission group（ P<0.05 or P<0.01）. The semi quantitative grading score by MSUS and total score of each group were positively correlated with DAS28 score，RF，ESR，and CRP（ P<0.05 or P<0.01）. The ROC curve analysis revealed that the semi quantitative grading score by MSUS had the largest AUC in diagnosing RA，with sensitivity and specificity of 96.89% and 79.54%，respectively，which were higher than those of serum RF，ESR，and CRP（ P<0.05）. Conclusion:The semi quantitative grading score by MSUS is positively correlated with DAS28 scores，RF，ESR，and CRP levels in RA patients，which has high sensitivity and specificity in diagnosing RA，thus having high diagnostic value for RA progression.