Abstract: The traditional method of temperature measurement is point-temperature measurement.To solve the difficulties of measuring the temperature field distribution in vacuum environment, based on the Raman scattering effect and optical time domain reflection technology(OTDR) of laser propagation in optical fiber, a distributed fiber Raman temperature measurement system is built to realize line temperature measurement.According to the distribution characteristics of temperature field in vacuum cryogenic tank, the selection and laying mode of sensing fiber and the connection of optical fiber flange through the tank are also studied.The results show that the distributed fiber Raman tempreature measurement system can work in vacuum cryogenic environment for a long time, and the performance is proved to be stable.It can indicate the temperature distribution on heat sink, and the accuracy meets the engineering requirement.