Diagnosis of lung cancer cannot be based on symptoms alone; more importantly, it is necessary to rely on objective auxiliary examinations, such as CT, fiberoptic bronchoscopy, etc. Ancillary examinations for lung cancer diagnosis can be broadly divided into the following categories: imaging diagnosis such as CT, MRI, PET, chest X-ray; endoscopy such as fiberoptic bronchoscopy and mediastinoscopy; and others such as serum tumor marker examination, sputum exfoliative cytology examination and so on. There are also some special examinations to determine whether lung cancer has distant metastasis, such as all bone scan (ECT), ultrasound of liver and adrenal gland, etc. The diagnosis of lung cancer is to determine whether the shadow (or occupancy) is lung cancer on the one hand, and the stage of the tumor can be initially determined on the other hand. CT and fiberoptic bronchoscopy are the two most important tools in the diagnosis of lung cancer. Most lung cancers have typical signs on CT and are not easily misdiagnosed. Some lung cancers have atypical signs and may require puncture. Fiberoptic bronchoscopy is an essential examination tool for central lung cancer, which can clarify not only the nature of the lesion, but also the extent of resection needed. In conclusion, lung cancer diagnosis is often not a simple process, and often requires a combination of various examinations and a certain degree of experience of doctors.