Abstract: ¹⁸F-FDG PET/CT has been widely used to diagnose benign and malignant lung tumors. ¹⁸F-FDG is not a targeted tumor malignancy indicator because highly metabolic inflammatory cells, such as macrophages, lymphocytes, and eosinophils, also exhibit high ¹⁸F-FDG uptake. Granulomatous lung inflammation is pathologically characterized by a large amount of metabolic inflammatory cell infiltration and is therefore the leading cause of false positive ¹⁸F-FDG PET/CT uptake. This review aims to improve the accuracy of ¹⁸F-FDG PET/CT technique in lung tumor diagnosis and help readers understand PET/CT technique and the mechanism of granulomatous lung inflammation.