High power operation of single-frequency Raman fiber amplifiers (RFA) is usually limited by the onset of stimulated Brillouin scattering (SBS).We present our theoretical investigation on RFA limited by SBS,based on the intensity equations combining SBS and stimulated Raman scattering.The influence of temperature gradients and strain gradients,which can broaden the SBS gain profile and thereby increase the SBS threshold,on the performance of RFA is discussed.Although tensile strain and temperature gradients can suppress SBS in RFA separately,the conditions are too rigorous to realize.A feasiblescheme for suppression of SBS in RFA is proposed using the temperature gradients together with tensile strain gradients along the fiber length,resulting in an increase of about 3 times of amplifier output power.The results of simulation provide a guide to suppress SBS in high power single-frequency RFA.