Absorption spectra, emission spectra and fluorescence time of 2F 5/2 energy level of Yb 3+ with different Yb 3+ ions concentration Er 3+ /Yb 3+ codoped SiO 2 Al 2O 3-La 2O 3 glasses have been measured. The effect of Yb 3+ ions concentrations on the absorption characteristics of Yb 3+ , stimulated emission spectra characteristics of Er 3+ , and the energy transfer efficiency from Yb 3+ to Er 3+ have been discussed. The result show that the optimal range of Yb 3+ ions concentration in this glass are from 3.94 to 5.92×10 20 cm -3 . In the optimal range of Yb 3+ ions concentrations, the maxim absorption coefficient of Yb 3+ is 9.8 cm -1 , the highest stimulated cross section of Er 3+ and the energy transfer coefficient η from Yb 3+ to Er 3+ are 0.64 pm 2 and 92% respectively.