Left subcostal refers to the left upper abdomen, lying flat pain side lying pain, most commonly seen in gastric ulcer, trauma and rib tumors. 1. Gastric ulcer: adverse drug symptoms and infection of Helicobacter pylori are the main causes of gastric ulcer, gastric ulcer will lead to gastric discomfort, when lying down the stomach contents are easy to reflux upward, gastric acid stimulation of the ulcer surface caused by the pain, lying on the side of the pain can be relieved or do not appear. 2. Trauma: when the left upper abdomen is injured by trauma and soft tissue injury, when the patient lies on the side, the soft tissue on the affected side will be reduced by pulling or compression, so that the left subcostal pain can be relieved when lying on the side. 3. Rib tumor: there is usually no obvious pain in the early stage of rib tumor, but this kind of disease will cause local bone weakness, when the patient is lying down, the lesion part will be pulled and compressed, which will cause pain in the ribs or the lower part of the ribs, and lying down on the right side can relieve the tension of pulling and pulling, so that there will be the case that the left subcostal bone is painful when lying down and there will be the case that the left subcostal bone is painful when lying down and there will be the case that the left subcostal bone is painless when lying down. Long-term existence of the left upper abdomen pain when lying down, side lying pain symptoms should be timely consultation, identify the cause of the disease, symptomatic, cause-specific treatment.