We experimentally investigated the temporal behavior of the forward and backward Stokes pulses from the stimulated Raman scattering in ethanol pumped by subnano second 6321 A pulse with amplitude modulation. It was found that both the forward and backward Stokes pulses have the same modulation period as that of the pump team, but the modulatity of the Stokes pulses is much larger. A theoretical explanation for the experimental results is presented.