Method of correcting PET image attenuation and PET/MRI devices are provided. In one aspect, an MRI image of a subject is segmented to obtain respective MRI sub-images corresponding to attenuation units of the subject, respective pseudo CT sub-images corresponding to the MRI sub-images are obtained based on an MRI-CT atlas, the respective pseudo CT sub-images corresponding to the MRI sub-images are spliced to obtain a pseudo CT image corresponding to the MRI image, and attenuation correction is performed for a PET image of the subject according to the pseudo CT image, wherein the PET image and the MRI image are obtained through a same scan process for the subject.