Early stage lung cancer patients usually have no obvious symptoms, while later stage may have symptoms such as cough, sputum, chest tightness, shortness of breath, headache and even bone metastasis, liver metastasis, adrenal metastasis and so on. As early lung cancer is mostly detected by medical checkups, it is clinically recommended that people over 40 years old should have medical checkups at least once a year in order to detect the disease and treat it as early as possible, so as not to miss the best time for treatment. Since it is difficult to detect early tumors in the back of the lung and small nodules less than 3cm by 2D chest radiography, it is clinically recommended that patients should choose low-dose CT during physical examination in order to avoid missed diagnosis.