Detailed experimental investigations on the amplification characteristics of back-injected simulated Brillouin scattering (SBS) seed laser in solid fused silica rod Brillouin amplifier under different pump power levels have been done, in which a master oscillator power amplifier (MOPA) single longitudinal mode Nd∶YAG laser with repetition rate of 400 Hz is used as pumping source, and a large aperture tapered fiber as SBS generator and solid fused silica rod as SBS amplifier. These characteristics include amplified SBS output power, amplification ratio of injected SBS seed laser, total SBS reflectivity, extraction efficiency of fused silica rod Brillouin amplifier, pulse width and beam quality versus SBS seed laser power. A maximum amplified SBS output power of 15.5 W, amplification ratio of 70, total SBS reflectivity of more than 50%, and extraction efficiency of 52% are obtained. Pulse width broadening and gain guiding have been observed. The experimental results indicate that the fused silica rod Brillouin amplifier has different amplification characteristics with small signal SBS seed laser and large signal SBS seed laser. Additionally, the degree of spatial superposition of SBS seed laser and pump laser and the pump power density in fused silica rod are found to be two important aspects which influence the amplified SBS output power.