The causes of left arm pain are cervical spondylosis, upper limb venous thrombosis, tennis elbow, etc., as follows: 1, cervical spondylosis: when the cervical disc tissue protrudes and presses on the cervical nerve root, there can be unilateral arm pain, sometimes accompanied by numbness of the fingers; 2, upper limb venous thrombosis: when the upper limb venous thrombosis is blocked will cause swelling and pain in the hand and arm, this situation should be carried out 3, tennis elbow: If the pain on the outside of the left arm, such as pain on the outside of the elbow joint, tennis elbow should be considered, which is mainly due to excessive household activities, causing excessive tension on the total stop of the extensor tendon, and therefore will be manifested as pain on the outside of the arm.