In this paper we report the results of spectroscopic intensity parameters of Er3+ in YAG:Er3+ single crystals. By using absorption spectra and Judd-Ofolt theory the experimental and theoretical oscillator strengths were caloulated. The rms deviation is only 1.9×10-7. Based on a least-square fit between experimental and theoretical oscillator strengths, the intensity parameters were determined. The results are Ωa = 0.19×10-20cm2, Ω4 = 1.68×10-20cm3; Ω6 = 0.62×10-20cm2. We then calculated probabilities of the Induced electric and magnetic dipole spoil taneoua radiative transitiong radiative lifetimes, high oscillator ,strength.Sj and branching ratios. The fluorescence spectra of Εr3+ in YAG:Ers+ coysxak were shown in the wave length range.