The effects of pumping pulse width on the energy output and the conversion efficiency of pulsed optically pumped FIB lasers have been studied experimentally. It is shown that both the energv output and the conversion efficiency can be improved notably at 66 μm and 385 μm lines from D2O and 496 μm line from CH3F by means of wide pulse pumping no matter whether they are stimulated Raman omission or not.