Peripheral lung cancer is defined as lung cancer that starts below the tertiary bronchus and above the respiratory fine bronchus. Adenocarcinoma is the most common type of lung cancer. Clinically, the symptoms of peripheral lung cancer are not obvious in the early stage, but it is already in advanced stage when the symptoms become obvious. In recent years, the application of multi-layer spiral CT has opened up a new way for early diagnosis of peripheral lung cancer. Based on the morphological size of the lesion, marginal signs, internal characteristics of the lesion and CT performance of adjacent tissues, the diagnosis of most peripheral lung cancers can be made. For a few cases with few or atypical basic signs, CT target scan should be performed on the lesion, and those who are still unable to determine the diagnosis should undergo CT-guided percutaneous puncture biopsy, transbronchoscopic lung biopsy or regular review within a short period of time to avoid misdiagnosis and omission of early peripheral lung cancer. After definite pathological diagnosis, staging diagnosis and molecular diagnosis should be made to guide clinical treatment. 1.X-ray examination This disease occurs in sub-segmental and sub-sub-segmental fine bronchial lung cancer, and the morphology of forming masses is relatively complicated. On the basis of mastering the pathology and X-ray signs of this disease, correct staging of this disease is not only helpful for diagnosis and differential diagnosis, but also can provide certain guidance for clinical treatment. 2.Multi-layer spiral CT examination Multi-layer spiral is an effective clinical examination and diagnostic technique for early peripheral lung cancer, which has high clinical application value. 3.CT target scan has a high diagnostic value for early peripheral lung cancer.