Abstract: Partial volume effect(PVE) and their influence factors for positron emission tomography(PET) were investigated with computer simulation and experiments. According to the theory of PVE formation, PET images of the hot lesions with different sizes under various system resolutions were simulated with computer program. The maximum recovery coefficient(RC), the average RC in the region of interest of which the size was the same as the real size of the hot lesion, and the full width at half maximum of the hot lesion on the images were calculated and compared with real experiments results. The results of simulation experiments quite agree with the real experiments. The variation curves of the maximum RC, average RC, and the ratio of the full width at half maximum of the hot lesion to the system resolution versus the diameters of the hot lesion, if the real lesion size is scaled in the system resolution, is independent of the system resolution.