Silicon photomultiplier technology based on Geiger-mode avalanche in p-n junction has made unforeseen progress for the last 7-8 years. With its high gain and high photon detection efficiency, it has shown that it could replace PMTs in many applications including time-of-flight Positron Emission Tomography (PET). Also, its magnetic immunity and compactness made it very suitable for PET-MR detector. With a short introduction about PET and PET/CT, time-of-flight PET-MR detector based on silicon photomultiplier will be presented from its selection, prototype test with discrete electronics, ASIC and a module design. Also, the system performance data is presented.