Abstract: The green fluorescence of U(Ⅵ) in CaF2 matrix was investigated in the temperature range 78-300·K with a N2 laser as an excitation source. The fluorescence spectrum can be interpreted as a no-phonon line with vibrational structure on the side. The temperature dependence of the no-phonon line is in agreement with theoretical calculation. The fluorescence lifetime of no-phonon line transition increases with decreasing the temperature and is 170 μs and 560 μs at 300·K and 78·K respectively.