ThestimulatedBrillouinscattering(SBS)thresholdaffectedbyrepetitionrateandpulsedurationinasinglefrequencynanosecondpulsedfiberamplifierisstudied.TheexperimentalresultsdemonstratethattheSBSthresholdcanbeimprovedeitherbyreducingtherepetitionrateorbynarrowingthepulseduration;however,theaveragepowermaybelimitedinsomecases.Otherwise,twoevaluationmethodsfortheSBSthresholdinthefiberamplifierarecomparedanddiscussed,aimingtoobtainamoreaccuratedescriptionfortheSBSthresholdinoursingle-frequencyamplifiersystem.