PET-CT integrates CT and PET, with CT providing precise anatomical positioning of the lesion and PET providing detailed molecular information on function and metabolism of the lesion, which is sensitive, accurate, specific and precisely positioned. The purpose of early detection of lesions and diagnosis of diseases. The accuracy of diagnosis is significantly improved. PET (Positron Emission Computed Tomography) is the full name of PET. It is one of the most advanced medical imaging technologies, and PET technology is the only technology that performs functional, metabolic and receptor imaging in an anatomical-morphological manner with non-invasive features. It is currently one of the best clinical tools used to diagnose and guide the treatment of tumors. PET-CT is suitable for the differential diagnosis of most benign and malignant tumors, early diagnosis, staging and grading of tumors and evaluation of systemic conditions; evaluation of efficacy before and after treatment by various means (including: differentiation of tumor remnants and scar tissue after surgery, changes in tumor lesions before and after radiotherapy and chemotherapy, differentiation of radioactive pneumonia and tumor recurrence, etc.) and the search for primary tumor foci and systemic monitoring of metastases. Identification of tumor with or without recurrence; providing a reliable basis for guiding tissue localization diagnosis and selecting the correct treatment plan and evaluating the efficacy; identifying biological target areas to guide precise treatment by linear gas pedal, gamma knife and other radiotherapy means. 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 greatly saves medical costs and fights for valuable treatment time. PET-CT is mainly used for malignant tumors, which have become the main killer of people’s health in China, and it is not uncommon for families to be impoverished because of their loved ones suffering from tumors. With the gradual maturity of PET-CT application, the clinical value of PET-CT will definitely be recognized and will play a greater role in clinical practice. The clinical value of PET-CT will be recognized and will play a greater role in clinical practice.