Positron emission tomography (Positron Emission Tomography, i.e. PET in brief) is a technique of medical localization diagnosis in frontier science that conducts functional, metabolic and receptor visualization with anatomic morphology and provides information of molecular level. It mainly utilize the primary substance metabolism process of the hyper-short-half-life isotope, which compose the human essential elements, such as O, N, C and F, etc. It has the characteristics of high sensitivity and minor trauma and can reflect physiological or pathological changes of humans at molecular level. At present, the fluorodeoxyglucose (FDG), a common developer used in clinical practice can mainly reflect human metabolic process of glucose. The clinical application of PET in oncology can be traced back to 1980's. Early application of PET has mainly been in diagnosis of indefinite and solitary nodus of the lung. With consummation of the technology, decrement of cost for examining preparation of ancillary drugs and materialization of the superiority, the clinical application of PET were gradually extended to the diagnosis, staging and surveiliance of curative effects, as well as detection of relapse or residual foci for tumors in large intestine, esophagus, breast, and head and neck, etc.