The SiPM is one of the core device of instruments like PET (PET-CT, PET-MRI), SPECT etc. Compared to traditional detector such as PMT, APD, the SiPM is superior in comprehensive properties. As a silicon-based detector, the SiPM is compact, magnetic field compatible, robust, and it owns excellent timing performance, signal-to-noise rate, easy use. The operating voltage of SiPM is lower than 30 V, as a comparison, the PMT or APD needs hundreds volt.