There are many reasons why patients experience pain in the left large arm, such as pain in the left upper limb area of the patient due to excessive strain, strain, cold, and other factors, resulting in old damage to the left biceps and triceps muscles. This arm pain will be gradually relieved after giving bed rest, reducing activities, treating the left upper limb with hot compresses, and performing herbal fumigation and other treatments. In addition, if the patient suffers from rotator cuff injury, frozen shoulder, cervical spondylosis, herpes zoster, etc., when moving the shoulder joint, it will also involve the pain in the arm area, accompanied by the limitation of shoulder joint movement and other conditions. Patients should be instructed to move their shoulder joints actively and passively, and at the same time to apply ointment to the shoulder and arm to relieve blood stasis, swelling and pain, or to take analgesic and blood-boosting drugs orally, which can improve the pain in the arm. Therefore, it is crucial for the patient to seek timely medical consultation after this phenomenon occurs. After a clear diagnosis by the doctor and timely adoption of correct treatment, the phenomenon can be cured or relieved quickly.