The diagnosis and treatment of lung cancer have made great progress in recent years, but the overall survival rate at 5 years after surgery is still less than 50%. The application of non-invasive imaging for diagnosis and accurate staging of lung cancer, and the formulation of appropriate individualized treatment plan and re-staging, efficacy assessment and prognosis judgment after treatment are of great importance to improve the survival rate of lung cancer patients. CT examination is the conventional imaging method to diagnose lung cancer, HRCT can provide the precise location, size, morphology, margins and internal features of lung occupancies, but there are limitations for qualitative diagnosis of lung nodules (especially isolated nodules).PET reflects the physiological metabolic state of lesions through their uptake of imaging agents for qualitative and quantitative diagnosis, but its spatial resolution is low.PET/CT integrates PET/CT fuses tomographic and functional metabolic images to achieve the complementary advantages of the two technologies, thus significantly improving clinical diagnostic efficacy and the accuracy of tumor diagnosis and staging. Most of the peripheral lung cancers are adenocarcinomas, and the typical HRCT presentation is a burr at the margin, a “vacuolation sign” within it, a pleural depression or pleural traction sign, and a peripheral “halo sign” with or without glass grinding. A few of them are small cell carcinoma, and HRCT shows smooth and sharp nodules or masses with multiple lobar signs. The SUVmax of PET-CT has a certain reference value in identifying benign and malignant lesions, and Bryant et al. found that if the SUVmax was 0-2.5, the probability of malignant pulmonary nodules was 24%; if the SUVmax was 2.6-4.0, the probability of malignant was 80%; if the SUVmax was >4.0, the probability of malignant nodules was 80%. If SUVmax>4.1, the probability of nodule malignancy was 96%. FDG metabolism differs among different pathological types of tumors, and SUVmax correlates with the pathological type of lung cancer. …… Therefore, for lung lesions with atypical performance on both HRCT and PET, in addition to observing their imaging performance and metabolic abnormalities, clinical anti-inflammatory treatment or short-term follow-up observation is required to improve the accuracy of diagnosis. Studies have shown that the larger the diameter of malignant nodules in the lung, the higher the SUVmax may be, and there is a linear correlation between the two. The staging of lung cancer is crucial for prognosis and treatment strategy. Some studies have shown that PET/CT is significantly better than CT alone in lung cancer staging and provides higher accuracy and specificity in lymph node staging, which has important implications for treatment plan selection, setting of radiotherapy target areas, and prognosis. FDG reflects abnormalities in focal glucose metabolism and is a non-tumor-specific imaging agent. The false positive and false negative of PET/CT may interfere with the localization and qualitative diagnosis of primary and metastatic lung cancer.