Sweet mouth is usually not a precursor of lung cancer, and it is not the first thing to consider lung cancer. Cough and sputum can be early clinical manifestations of lung cancer. Lung cancer is a malignant tumor of respiratory system caused by heredity, smoking and environment. In the early stage of the disease, patients may have non-specific clinical symptoms such as cough, sputum, fatigue, fever, etc. With the development of the disease, hemoptysis, chest pain, dyspnea, distant metastasis and other manifestations may appear. However, there is no symptom of sweet mouth. Usually, sweet mouth can be caused by digestive tract dysfunction, resulting in increased amylase content in saliva; or diabetes and other diseases. Patients should go to the hospital for standardized diagnosis after the occurrence of uncomfortable symptoms, so that the cause of the disease can be clarified in time and the symptoms can be treated.