Abstract: PET-CT and magnetic resonance diffusion-weighted imaging(DWI) are two types important imaging modalities in tumor detection, the former could provide functional metabolism information, such as glucose metabolism, amino acids metabolism and so on.While the latter could offer the water molecules motion information in tissues.The two modalities both have advantages, disadvantages and indications of themselves.We will obtain more morphology and metabolism informations while the two modalities were combined favorably.The combination of the two were useful to decide the quality of local lesions and systematic stage, and to increase the diagnostic accuracy, that could provide the most effective informations for clinic to choose optimal treatment plan.