PET-CT is the world’s most advanced medical imaging diagnostic equipment, which is called “the crown of modern medical technology”. With the features of sensitivity, accuracy, specificity, and precise localization, PET can obtain tomographic images of the whole body in all directions in a single image, so that the overall condition of the whole body can be understood at a glance, and the purpose of early detection of lesions and diagnosis of diseases can be achieved. The emergence of PET-CT is another revolution in medical imaging and has been widely recognized by the medical community as the greatest invention of the twenty-first century, with a highly sensitive and accurate localized imaging system for tumors. The application of PET-CT is mainly reflected in the following aspects: a. PET-CT can make early diagnosis and differential diagnosis of tumors, identify whether tumors have recurrence or not, stage and re-stage tumors, search for tumor primary and metastatic foci, guide and determine the treatment plan of tumors, and evaluate the efficacy of treatment. Among tumor patients, a considerable number of patients have changed their treatment plan after PET-CT examination due to clear diagnosis; PET-CT can accurately evaluate the efficacy, timely adjust the treatment plan and avoid ineffective treatment. Overall, it can greatly save medical costs and buy valuable treatment time. Second, PET-CT can accurately locate epileptic foci, and is also a unique examination method for diagnosing depression, Parkinson’s disease, Alzheimer’s disease and other diseases. Third, PET-CT can identify whether the heart muscle is alive or not, and provide objective basis for the need of surgery. PET-CT is also valuable for the diagnosis of early coronary heart disease. PET-CT is also a means of health checkup, which can complete the whole body detection in one image, and can detect tumors and heart and brain diseases that seriously endanger people’s health at an early stage, so as to achieve the purpose of early treatment of diseases and prevention of diseases.