Glasses with the compositions of (77-x)GeO2-xGa2O3-8Li2O-10BaO-5La2O3(x=4,8,12,16) doped with 8.0mol% of Tm3+ were fabricated. The spectroscopic properties and thermal stability were investigated experimentally with increasing Ga2O3 content from 4mol% to 16mol%. It is noted from differential thermal analysis curves that the thermal stability of the glasses are improved by increasing Ga2O3. According to Judd-Ofelt theory, the Judd-Ofelt strength parameters (Ω2，Ω4，Ω6) of Tm3+-doped GeO2-Ga2O3-Li2O-BaO-La2O3 were calculated, by which the radiative transition probabilities, fluorescence branching ratios and radiative lifetimes were obtained. The emission spectra of Tm3+-doped germanate glasses and the effects of Ga2O3 on the emission properties were investigated with 808nm laser diode excitation. The fluoroscopic intensity and the maximum stimulated emission cross section first decrease along with the increase of Ga2O3 content from 4mol% to 16mol%, and reach a minimum at Ga2O3 content of 12mol%, and then increase. The effects of Ga2O3 on the glass structure and the spectral parameters were also preliminarily investigated.