〔Abstract〕 Objective To quantity the degree of acromial droop tilt and explore its correlation and diagnostic value for subacromial impingement syndrome. Methods The degree of quantification of shoulder tilt and droop(including Angle α、β、γ、Δ、ε、ζ) was analyzed by preoperative MRI of 40 patients undergoing arthroscopic surgery(experimental group) and 40 healthy shoulder MRI(control group).The correlation and difference of each quantitative index in each group and group were compared to discuss their diagnostic value for rotator cuff injury and subacromial impingement syndrome. Results There was no significant difference between the patients group and the control group in the acromion droop and tilt correlation the independent sample T test of angle α(P>0.05), respectively, and the difference was statistically significant(P<0.05). The region below the ROC curve of β,γ,Δ,ε,ζ were 0.677, 0.864, 0.707, 0.848, 0.886, respectively, and the region below the ROC curve of β and ζ combined was 0.906, indicating excellent diagnostic performance. Conclusion Acromial droop and tilt correlation angle have certain value in the diagnosis of subacromial impaction syndrome. The quantitative indexes γ,ε,ζ have significant significance in the diagnosis of SAIS, and the combined diagnosis performance of β and ζ is better.