In the clinic, the patient has the phenomenon of pain under the left side of the rib cage when he breathes, and there are many diseases that cause this pain phenomenon. For example, the patient’s left rib cage, due to the subcutaneous easily accessible, and attached to the muscle group is less, in the external force or a long time cold, can be injured to the local intercostal muscles, resulting in muscle damage, the patient will have this phenomenon. In addition, the patient’s left rib, also in the external force, also prone to rib fracture, the patient in the breathing will pull, stimulate the fracture end, the patient will feel localized pinprick pain, and there will be localized swelling, subcutaneous bruising, thoracic compression test is positive, you can take a local X-ray, can make a clear diagnosis. Therefore, patients with pain phenomenon, we should consult the doctor as soon as possible, after the correct treatment can cure this phenomenon.