The difference between rotator cuff strain and frozen shoulder can be identified by history, symptoms, and imaging tests. 1. Medical history: Most rotator cuff strains have a history of indirect violence such as propping up the ground with the hands when falling, etc. In the elderly, rotator cuff tissues may undergo degenerative changes, and there are often triggers such as lifting and pulling heavy objects and excessive activities. Primary frozen shoulder is a self-limiting aseptic inflammation of the soft tissues around the shoulder joint, the cause of which is unknown. It can also be secondary to upper extremity trauma or surgery, such as shoulder dislocation, chronic rotator cuff injury. 2. Symptoms: Typical symptoms of rotator cuff injury are night pain, back and hand pain, and pain aggravated when the shoulder joint is abducted at 60°～120°, which is also called “pain arc”, and passive activities are often normal. Typical symptoms of frozen shoulder are pain around the shoulder joint and limitation of activities, which are characterized by stiffness of the shoulder joint, inability to raise the arm, and pain when rotating the shoulder. 3. Imaging: Imaging can show rotator cuff tear in rotator cuff injury. Frozen shoulder itself can be caused by the fibrosis of rotator cuff space and edema of anterior inferior joint capsule, and the imaging can also have no abnormal manifestation, and shoulder arthrography can be used to assist the diagnosis. Rotator cuff strain and frozen shoulder can also be differentiated by other aspects such as age. It is recommended to go to the hospital as soon as possible to clarify the cause of shoulder discomfort so as to avoid delay in treatment.