The causes of right arm pain at night are as follows: 1. Rotator cuff injury: When rotator cuff injury or tear occurs, it can easily cause shoulder joint pain, accompanied by weakness in supination, and a typical feature of rotator cuff injury is pain at night; 2. Frozen shoulder: Pain around the shoulder joint can occur, including the shoulder deltoid area, outer upper arm, inner upper arm, which is the axillary area, the front of the shoulder joint and the scapular area, which can be particularly pronounced at night; 3. Tumor disease of the right arm: For example, giant cell tumor of the right arm or osteosarcoma can be characterized by pain at night.