Abstract: Recently, combined PET/CT is a new imaging system which enable acquire co-registered anatomic and biological function images in a single scanning session.PET/CT is valuable for improving tumor localization, planning of radiation therapy, defining biopsysite and evaluating response to therapy.CT can also provide low-noise CT-based attenuation correction for PET emission scan.The design and performance, clinical application, advantages and some technical limitation of a combined PET/CT scanner were summarized briefly in this paper.