Objective To determine the change in humeral head anterosuperior migration after releasing the coracoacromial l igament in shoulders from cadavers with simulated intact or irreparable teared rotator cuff, to provide biomechanical basis for preserving the coracoacromial l igament or not during hemiarthroplasty. Methods Twelve freshfrozen cadaveric glenohumeral joints of adult preserving the scapula, upper 2/3 of the humerus, articular capsule and the coracoacromial l igament, were divided into 2 groups. The suprascapularis was preserved in group A (6 shoulders) and excised in group B (6 shoulders). Positioning the joint in a combination of 30° extension, 0° abduction and 30° external rotation, and imposing a 50 N axial compressive load to the humeral shaft, the anterosuperior displacement of the humeral head weremeasured before and after excising the coracoacromial l igament. Results In group A, the displacement of the humeral head was (5.96 ± 0.77）mm with intact coracoacromial l igament and (6.83 ± 0.84）mm after transecting the l igament. In group B, the displacement of the humeral head was (8.07 ± 2.46）mm with intact coracoacromial l igament and (9.92 ± 3.29）mm after transecting the coracoacromial l igament. So the mean increase of anterosuperior migration of the humeral head was (0.88 ± 0.34) mm (P lt; 0.01) in group A, and (1.85 ± 0.99) mm (P lt; 0.01) in group B, which was greater than the former (P lt; 0.05). Conclusion The coracoacromial l igament restrained anterosuperior translation of the humeral head, especially for patients with rotator cuff deficiency, so it should be preserved as far as possible during hemiarthroplasty.