In order to validate the effect of beam smoothing and to get the radiation characteristics of gas-filled hohlraum, the energy fraction of backscattering light and the streaked spectrum are measured by the backscattering measurement system on Shenguang-III prototype facility. The results indicate that in the current experimental conditions, beam smoothing can effectively inhibit the backscattering light fraction. The energy fraction of backscattering light is 25%~35% without beam smoothing, and the energy fraction decreases to 2%~4% with beam smoothing. The fraction of stimulated Raman scattering in gas-filled hohlraum increases markedly from 2%~4% in empty hohlraum to 10%~13%. The results of spectrum measurement indicate that beam smoothing can improve the uniformity of plasma. Stimulated Raman scattering occurs at the early stage of the laser effect for gas-filled hohlraum, but it occurs at the late stage for empty hohlraum.