Brillouin amplifier was numerically simulated by using the theoretic model of transient stimulated Brillouin scattering. Wehave oblained the depleted pump energy extract efficiency, Stokes seed amplification factor, seed beam pulse\|width compression ratio and pump beam pulse\|width compression ratio versus the ratio of seed to pump energy. Experiment was done so as to verify the theory. The theoretical calculation was in good agreement with experimental results.