Glasses with the compositions of (90-x)GeO2-xNb2O5-10Na2O(x=1,2,4,6,8 molar ratio)doped with Tm2O3 at the same concentration (4wt%) and 86GeO2-4Nb2O5-10Na2O dore at different concentrations were fabricated respectively by conventional melting method.The effects of Nb2O5 content on glass stability,fluorescence strength and J-O strength parameters were studied.According to the Judd-Ofelt theory,the J-O strength parameters (Ω2, Ω4, Ω6) of Tm3+ in different Nb2O5 concentration were calculated,with which the radiative transition probabilities,branching ratios and radiative lifetime were obtained.Meanwhile,according to the McCumber theory,the absorption and emission cross-sections corresponding to the 3F4→3H6 transitions of Tm3+ at 1.8 μm were obtained.The gain cross section was calculated by using the emission cross-section,absorbtion cross section and Tm3+ concentration.The fluorescence features (under 808 nm LD excitation) at ～1.47 and ～1.8 μm of Tm3+-doped glasses of different concentrations were studied.The fluorescence intensity at ～1.8 μm reached to the maximum when the Tm2O3-doping concentration was about 3wt%,and then decreased as the doping concentration increased further.The fluorescence intensity at ～1.8 μm reached to the maximum when the Nb2O5 content in glass composition was about 2 mol%.The effects of Nb2O5 content on the glass structure and the spectra properties were also discussed.