Glasses with the compositions of 0.3SiO2-0.1Al2O3-0.1AlF3-0.5PbF2 doped with different Tm3+ concentration (x=0.5 mol%,1.0 mol%,2.0 mol%,3.0 mol%) were fabricated by conventional melting method. According to the absorption spectra and the Judd-Ofelt theory, the J-O strength parameters (Ω2,Ω4,Ω6) of Tm3+ were calculated, by which the radiative transition probabilities, fluorescence branching ratios and radiative lifetimes were obtained. The infrared emission spectra (with 808 nm laser diode excitation) at ～1.47 μm and ～1.8μm of various concentration Tm3+-doped glasses were studied. The emission intensity at 1.8 μm reaches to the maximum when the Tm3+-doping concentration is near to be 2.0 mol% and then decreases at higher concentration. The mechanism of the change of the fluorescence intensity was explained from the cross-relaxation effect and the concentration quenching effect of Tm3+. The absorption cross section of 3H6→3F4 transition and the stimulated emission cross section of 3F4→3H6 transition of Tm3+ have also been calculated according to McCumber theory.