Pain in the middle of the left side of the back should be considered in the following aspects:1. Diseases of the back itself, such as trauma, inflammation, tumors and other diseases, can appear in the middle of the left side of the back pain, and there can be obvious pressure pain, and if necessary, CT or MRI should be done for further clarification.2. Lung diseases, such as pneumonia, tuberculosis, lung tumors and other diseases, especially the foci are closer to the back when the pain is more obvious when coughing or deep breathing. The pain is more obvious when coughing or deep breathing, often combined with coughing, coughing up sputum, chills, fever and other symptoms. 3, pleural diseases, such as pleurisy, pleural tumors, can also appear in the middle of the left side of the back pain.