Pseudo-Random　Binary　Sequence　(PRBS)　phase　modulation　is　an　effective　method　for　suppressing　the　stimulated　Brillouin　scattering　(SBS)　effect　generated　by　narrow-linewidth　fiber　lasers　during　amplification.　We　noticed　that　backward　time-domain　pulses　were　generated　when　using　PRBS　modulation　signals　in　fiber　amplification.　In　this　paper,　the　time-domain　dynamic　characteristics　of　the　forward　output　laser　and　the　backward　Stokes　light　after　PRBS　phase　modulation　were　studied　theoretically.　Through　analyzing　the　transient　SBS　three-wave　coupling　theory　and　combining　it　with　the　SBS　accumulation　time　constant,　we　knew　that　the　forward　and　backward　high-intensity　pulses　were　caused　by　the　long　dwell　time　of　the　PRBS.　For　this　purpose,　we　provided　a　new　method　for　suppressing　high-intensity　pulses　caused　by　a　long　dwell　time;　namely,　we　modified　the　maximum　length　sequence　(MLS)　of　PRBS　signals　to　eliminate　the　long　dwell　time,　took　the　PRBS-9　signal　at　1　GHz　as　an　example,　and　then　used　MLS1　modulation　and　MLS2　modulation　to　compare　them　with　unoptimized　PRBS　modulation.　The　output　laser　peaks　of　the　MLS1　and　MLS2　signals　were　reduced　from　+/-　55%　to　+/-　25%　and　+/-　10%　relative　to　the　original　PRBSs,　respectively,　and　the　peaks　of　Stokes　light　were　reduced　from　39%　to　19%　and　11%,　respectively.　Additionally,　we　experimentally　verified　that　the　rational　optimization　of　the　sequence　did　not　reduce　the　SBS　threshold.　The　results　provided　a　new　method　for　suppressing　high-intensity　pulses　during　the　amplification　of　a　PRBS　phase-modulated　laser,　which　played　an　important　role　in　the　output　stability　of　high-power　narrow-linewidth　fiber　amplifiers.