The pain on the lateral side of the arm can be caused by the following reasons: first, cervical spondylosis, cervical spondylosis can compress the nerve roots, radioactive pain on the lateral side of the arm, especially at night when sleeping under pressure and cold pain is very significant, then the cervical spine X-rays, MRI to diagnose and early treatment. Second, dermatomal neuritis, when the dermatomal nerve on the lateral side of the arm has chronic inflammation, there can be pain in the skin of the area it innervates, which can be tingling or numbness, often the size of a palm, then early diagnosis should be made by physical examination, early oral nerve-nourishing drugs and physical therapy. Thirdly, when the shoulder joint has frozen shoulder or rotator cuff tears, the pain in the proximal or distal part of the arm can also be radiated, and it is necessary to check the MRI of the shoulder joint and the examination of the shoulder joint for diagnosis and early treatment.