Lung cancer has been one of the main death reasons of human being died because of cancer. The incidence and death rate of lung cancer have been increasing rapidly in recent years. X ray and CT (computer tomography) scan of thorax can diagnose most lung cancer,but there are some difficulties on diagnosis of early-stage lung lesions. PET(positron emission tomography) has high sensitivity and specificity on early diagnosis,stage and curative effect evaluation of lung cancer,with poor space distinguishing. PET/CT can make up the drawbacks metioned above. PET/CT can provide the special imaging mode information of both PET and CT. This is a review about the application of PET/CT in the diagnosis of lung cancer.