Objective: To evaluate the association between rotator cuff tear and the proximal migration of humeral head.Methods: In this research, we retrospectively selected 30 patients with unilateral rotator cuff tear in Peking University People’s Hospital from September 2015 to May 2016, who received magnetic resonance imaging (MRI) and X-ray of the painful shoulder before enrollment in this study, the duration between the two examinations was no longer than 1 week, and also there was no past history of surgery in the selected shoulders. There was no other exclusion criteria. Upward migration index (UMI) was the ratio between the distance of humeral head center to the lower surface of acromion, and the radius of humeral head circle, which could help to minimize the effect of anatomy difference and imaging magnification, compared with the traditional acromiohumeral distance (AHD). Then we introduced this index to stratify the selected 30 patients into 3 groups , and each group contained 10 patients, UMI of group 1 was >1 and ≤1.2, UMI of group 2 was >1.2 and ≤1.4, UMI of group 3 was >1.4. As the supraspinatus was most commonly affected by pathological change among the four rotator cuff tendons, we took it as the research object. Then we used the Spearman correlation analysis to evaluate the relationship between UMI and fatty degeneration, rotator cuff tear size and the thickness of ruptured supraspinatus tendon from X-ray and MRI.Results: In the A-P view, the average UMI was 1.33 (1.02-1.51, SD: ±0.22). UMI and the tear size had a significant negative correlation (R=-0.584, P<0.01), and also there was a negative correlation between the fatty degeneration of the supraspinatus (R=-0.312, P=0.033). However, there was no correlation between UMI and the thickness of ruptured supraspinatus (R=0.127, P=0.071).Conclusion: UMI is related with the fatty degeneration of supraspinatus and the tear size. The reduction of UMI is a predictable and reliable mark of rotator cuff tear and degeneration in clinic. Physicians can use physical examination and X-ray first when facing the patients with shoulder pain, which is convenient and helpful for evaluating rotator cuff tears.