We measured the emission spectra, absorption spectra and the exited state life time of Cr 4+ :YAG and Cr 4+ :Mg 2SiO 4 crystals at room temperature and liquid nitrogen temperature respectively. The variation of the integral fluorescent intensities at the two different temperature was obtained. Considering it with the variation of the exited state life time, we could draw a conclusion that in the range of 77 K to 300 K, the influence of temperature on the emission cross section of Cr 4+ is relatively small. The change of the fluorescent intensity is mainly because of the change of non emissive relaxation rate with temperature.