The diagnosis methods of lung cancer are divided into direct diagnosis and indirect diagnosis. The so-called direct diagnosis means that the tissues with lesions can be taken by various methods and the tumor cells can be found through histocytopathology to confirm the diagnosis of lung cancer. This is also the gold standard for lung cancer diagnosis. Indirect method is to find lesions from imaging, serum tumor markers, functional imaging, etc., and diagnose lung cancer from its characteristics. Because there is no real histopathological evidence, it is subject to error and cannot be used as the gold standard. Direct diagnostic methods include: bronchoscopic biopsy, sputum to find tumor cells, pleural fluid to find tumor cells, lung puncture biopsy, thoracoscopic lung biopsy, mediastinal or superficial lymph node biopsy, etc. Indirect diagnosis methods include: chest X-ray (X-ray is the most common and important means to diagnose lung cancer. The location and size of lung cancer can be understood through X-ray examination. In early stage lung cancer cases, although the mass is not yet visible on X-ray, local emphysema, pulmonary atelectasis or infiltrative lesions or inflammation in the lung adjacent to the lesion due to bronchial obstruction may be seen), chest CT (it is valuable for early detection of lung cancer lesions in areas hidden from general X-ray examination, such as the lung tip, supra-diaphragm, paraspinal, pleura near the chest wall, posterior to the heart, mediastinum, etc., and for clarifying whether the mediastinal lymph nodes are enlarged or not), PET (it is very valuable for diagnosing lung cancer in the early stage. It is of great diagnostic value), PET (which can detect unexpected extra-thoracic metastases and can make the preoperative period more accurate) and other functional imaging examinations.