Sputum exfoliative cytology is a special test for difficult lung diseases in the Department of Respiratory Medicine, and is mainly used to rule out whether lung nodules, inflammation, or occupancies are caused by tumors. The cost of the test is approximately 150 yuan for one visit, based on each morning coughing up sputum and sending the specimen, and three consecutive visits are required. If the sputum is positive for cytology, that is, abnormal tumor cells are found, the diagnosis of early stage malignancy is most likely confirmed. If sputum exfoliative cytology is negative, but chest imaging, including CT examination, suggests lung cancer and other neoplastic diseases, sputum exfoliative cytology negative still cannot completely exclude the diagnosis of lung cancer, and further chest enhancement CT, fiberoptic bronchoscopy and other examinations are needed to avoid missed diagnosis and misdiagnosis. Sputum exfoliative cytology examination is necessary as a basic examination for tumor screening in respiratory medicine, but its positive rate depends on whether the tumor cells are shed or not, if not, it can cause false negative.