High power operation of single-frequency Raman fiber amplifier (SF-FRA) is usually limited by the generating of stimulated Brillouin scattering (SBS). Based on the intensity equations combining SBS and stimulated Raman scattering (SRS), the limitation action to the output power of SF-FRAs for SBS is studied, the influence of different strain distributions to SBS inhibition is compared and an optimal solution of strain distribution is proposed. The simulation results indicate that strain gradients along Raman gain fibers can broaden the SBS gain profile and thereby suppress SBS. The location, stage number, value and length have the optima in the fibers′ receivable range of strain. The threshold of output power of SF-FRA can be increased about 100% under the optimum condition.