Lung cancer is the most threatening malignant tumor to human health and life. In China, lung cancer has become the first cause of death from malignant tumors. We can classify lung cancer into stage I, stage II, stage III and stage IV according to the size of the tumor, the presence or absence of metastasis of hilar and mediastinal lymph nodes, and the presence or absence of metastasis of the contralateral lung and distant organs outside the lung, among which, stage I lung cancer is further divided into stage Ia and stage Ib. Clinically, many early stage I lung cancers have a 5-year survival rate of nearly 90% after thoracoscopic or minimally invasive lobectomy, while the 5-year survival rate of late stage lung cancer is only about 10%. Therefore, early diagnosis and early treatment are crucial to improve the 5-year survival rate. Unfortunately, most of the lung cancer patients who come to the clinic are in the middle and late stages, losing the best time for treatment. Therefore, it is more urgent to actively diagnose lung cancer at an early stage by popularizing lung cancer medical checkups to increase the chance of surgical cure and thus reduce lung cancer mortality. Then, why is lung cancer mostly found in late stage? First of all, the symptoms of early stage lung cancer are not obvious or difficult to attract people’s attention. Most lung cancer patients do not have any symptoms in early stage, and even if some patients have symptoms, their symptoms often lack characteristics and are difficult to attract the attention of patients or even doctors, which is an important reason why lung cancer patients cannot be detected at an early stage. On the other hand, the means to detect early lung cancer are limited; X-ray examination is difficult for early lung cancer with very small lesions, and in some cases, the detection rate is very high due to the special location of lesions. Recently, the results of a large-scale observational study conducted in the United States showed that low-dose spiral CT is the first choice for early screening of lung cancer. In recent years, with the popularization and advancement of imaging technology, especially CT technology, the detection rate of ground-glass opacity (GGO) in the lung has gradually increased, which refers to a mildly increased density, focal cloudy shadow with clearly discernible vascular and bronchial textures on CT images. Various causes such as inflammation, fibrosis, atypical adenomatous hyperplasia (AAH) and early lung cancer (especially bronchioalveolar carcinoma (BAC)) can cause confined changes in the lungs. AAH is usually considered as a precancerous lesion of lung cancer. Many scholars in China and abroad believe that focal ground-glass nodular (fGGN) in the lung is closely associated with early lung cancer, especially BAC. The management of focal GGN is complicated, mainly because its diagnosis is very tricky, especially for clinically asymptomatic fGGN found on physical examination. since fGGN may be the only early imaging manifestation of BAC, it is necessary to perform high-resolution CT to further confirm the diagnosis in patients with suspected fGGN on plain CT in clinical practice. Currently, surgery is still the treatment of choice for early stage lung cancer. According to statistics, for early-stage lung cancer patients with poor cardiopulmonary function or comorbid diseases, sublobar resection can also achieve a five-year survival rate similar to that of lobectomy, and the postoperative quality of life is better than that of lobectomy. In conclusion, with the development of screening methods and examination techniques, “early detection, early diagnosis and early treatment” of lung cancer is possible. We call on everyone to pay attention to annual health check-ups and to have a low-dose spiral CT examination of the chest during health check-ups for people with high risk of lung cancer, which can help to detect early lung cancer and get early and effective treatment.