This paper proposes a method based on stimulated Brillouin scattering (SBS) for reshaping a temporal Gaussian waveform into a temporal high-intensity step waveform. The theoretical analysis showed that the reshaped temporal waveform depended on the phonon lifetime, the Brillouin gain coefficient, the interaction length between the Stokes and the pump pulse, and the pump energy. It further showed the dynamic evolution of the reshaped temporal waveform with these four parameters. By optimizing these parameters, a temporal step waveform with an intensity of 36.92 MW/cm2 was obtained in the experiment.