Nodules under the left side of the diaphragm can usually be caused by diseases such as pneumonia, tuberculosis, pulmonary nodular disease, or tumors, which require prompt medical treatment once detected. Nodules under the left side of the diaphragm are mostly secondary to respiratory infections or pleurisy, and most of the localized nodules are located around the lung tissues or under the pleura, and if sputum examination is performed and Mycobacterium tuberculosis is found to be positive, then it is presumed that the nucleus is due to infection by Mycobacterium tuberculosis, but the possibility of pulmonary tuberculosis still needs to be ruled out. Enhanced CT examination of the chest can be carried out when necessary, if the nodules are of mixed density or their solid components are increased, then the possibility of malignant tumors cannot be excluded, including primary and metastatic lung cancer, and biopsy should be carried out in time in order to clarify the cause of the disease, and surgical resection of the lesions should be selected according to the pathological results.