The high quality Na5Lu9F32 single crystals with different Tm3+ concentrations ranging from 0.5 to 4 mol% were grown successfully by an improved Bridgman method. The fluorescence spectra and decay curves at 1.86 μm were measured under the excitation of 790 nm LD to study the luminescent properties of the crystals and the energy transfer process between Tm3+ ions. The 1.86 μm emission intensity gradually increases to the maximum value when the Tm3+ concentration increases to around 1.95 mol%. Nevertheless, it decreases fleetly with the Tm3+ concentration further increase from 2.0 mol% to 4.0 mol%. The maximum stimulated emission cross section at 1.86 μm is also calculated to 0.80×10－20 cm2. The 1.86 μm fluorescence lifetime of Tm3+∶3F4 level decreases with the increase of Tm3+ doping concentration. The concentration quenching effect of Tm3+ ions and the cross relaxation energy transfer process between Tm3+ ions are mainly in charge of the variety of the 1.86 μm emission.