There is no specific time limit for how long it takes for a cough to be lung cancer. Cough is just a common symptom of the respiratory system with many causes, and lung cancer is just one of them. Early stage lung cancer patients can have cough, which is the main clinical symptom of lung cancer. Lung cancer patients’ cough is mostly irritating dry cough, which is more violent, and sometimes they can cough up purulent sputum and blood in sputum. Therefore, if cough and sputum cannot be relieved after regular treatment for more than two weeks, attention should be paid to them, especially for patients with high risk factors of lung cancer, and when accompanied by coughing up blood, they should improve chest CT, bronchoscopy and other examinations at an early stage in order to exclude the existence of lung cancer. Since the cough of lung cancer patients is mostly chronic, patients with chronic cough for more than 8 weeks should be screened for lung cancer, especially bronchoscopy, in order to exclude the presence of endobronchial lesions. It should also be noted that some lung cancer patients may not have cough, and the presence of lung cancer can be detected through routine physical examination, especially CT examination of lung, so the duration of coughing cannot be used to judge whether lung cancer exists or not.