Abstract: The spatial resolution of PET can reach 4-5mm in clinic, but it can not compare with X-ray, CT, MRI and other modality, and consequently restrict the application of PET in some clinical area, especially the inaccurate delineation of target volume in radiotherapy plan. Lots of factors can affect the resolution of PET, one of them is the smear caused by the motion of respiratory. The spatial resolution can be improved after the compensation of respiratory movement in order to enlarge the clinical application of PET. One of the compensation methods is respiratory gating.