In order to study whether the silicon photomultiplier (SiPM) can work properly at low temperatures, the reverse voltagecurrent (IV) characteristics of two typical SiPMs were tested and analyzed under different temperatures by liquid nitrogen refrigeration. The results showed that the maximum overvoltage ranges (VB~Vb) of the two SiPMs vary greatly with temperature, and the condensation of trace water vapor only has obvious influence on the IV characteristics of unencapsulated SiPMs only between breakdown voltage(Vb) and run away voltage(VB). The SiPMs working at low temperatures require lower concentration of defects and traps. When applying SiPM in low temperature environment, one should not only observe the leakage before breakdown, but also closely monitor the current of SiPM when the bias is in Vb~VB.