We obtain the output of a 284 ps pulse duration without tail modulation based on stimulated Brillouin scattering (SBS) pulse compression pumped by an 8 ns-pulse-duration, 1064 nm-wavelength Q-switched Nd:YAG laser. To suppress the tail modulation in SBS pulse compression, proper attenuators, which can control the pump energy within a rational range, are added in a generator-amplifier setup. The experimental result shows that the effective energy conversion efficiency triples when the pump energy reaches 700 mJ to 51%, compared with the conventional generator-amplifier setup.