In order to solve the application problem of fiber grating in low temperature environment, based on the sensing theory of fiber Bragg grating(FBG), through in-depth analysis of the changes of the thermo-optical coefficient and thermal expansion coefficient of FBG at the range of -60~25 ℃, and two unsealed FBGs is used for experimental verification, the response of FBG in low temperature environment is obtained in this paper. The results show that FBG has good response and repeatability in low temperature environment, which has important guiding significance for the application of FBG in low temperature environment.