Abstract: PET-CT multimodality imaging has become an essential tool for diagnosis, staging and therapeutic evaluation for malignancy.But MRI has better soft tissue resolution than CT, and provides a variety of functional imaging, multi-sequence and multi-parameter imaging, and has no radiation damage.The integration of plentiful information from MRI and molecular information provided by PET is expected to become a new dual-mode imaging tool which will play a very important role in basic and clinical research.However, many challenges are existed in the combined PET and MRI technology, and it has become a focus in molecular imaging research in recent years, and has made significant progress.This paper overviews the progresses of PET-MRI integration technologies and devices, preliminary applications and multimodality probes.