In low temperature environment, the thermal expansion coefficient and thermal optical coefficient of fiber Bragg grating (FBG) material will change, which will affect its temperature sensing characteristics. In this paper, the temperature sensing characteristics of bare FBG sensors and brass tube-encapsulated FBG sensors were studied experimentally. The results show that in the temperature range of 80~300K, the sensitivity of the bare FBG temperature sensor is 6.43pm/K and the linearity is 0.974, and the relationship between temperature and fiber grating center wavelength is nonlinear in the temperature range of 80~230K. The brass tube-encapsulated FBG temperature sensor has a sensitivity of 26pm/K and a linearity of 0.996 in the whole temperature range, which is greatly improved compared with that of the bare FBG temperature sensor. Comparative experiments show that the encapsulating of fiber Bragg grating can not only improve its temperature sensitivity and linearity, but also improve its temperature sensing characteristics.