In order to investigate the temperature dependence of micro-nanofiber Bragg grating (MNFBG) in application, we simulate the relationship between reflection wavelength and temperature of MNFBG which is surrounded with liquids with different refractive indexes, and MNFBGs surrounded with replaceable encapsulating liquids are fabricated and used in experiments. In experiments, the variations in reflection spectral and its center wavelength with temperature of encapsulating liquids can be obtained when we encapsulate the MNFBG with distilled water and matching liquids with different reflective indexes. Research results show that the shape and the moving direction of reflection spectra can be effected by the encapsulating liquids with different properties in the same temperature changing process, which is different from the ordinary fiber Bragg grating (FBG). The reflection spectral shape of the ordinary FBG almost does not change when temperature is increasing, but its center wavelength increases with the temperature increasing linearly. The larger the refractive index and the thermo-optic coefficient of the encapsulating liquids are, the more nonlinearity the spectral wavelength shifting with temperature changing is. When the MNFBG is surrounded with the liquid with the refractive index of 1.456 and the thermo-optic coefficient of 4×10-4 ℃-1, the temperature sensitivity of the reflection wavelength can reach up to -50.3 pm/℃. These spectral characteristics of MNFBG are connected with the surround liquid, the temperature and the size of FBG. Through effectively controlling these correlative factors, more functional applications of FBG will be realized in different fields.