When　designing　a　fiber　laser,　it　is　difficult　to　achieve　both　narrow　linewidth　and　high　power　due　to　nonlinear　effects,　especially　stimulated　Brillouin　scattering　(SBS).　However,　using　the　pseudo-random　binary　sequence　(PRBS)　phase　modulation　technique,　SBS　can　be　effectively　suppressed　in　narrow-linewidth　fiber　lasers　during　amplification.　In　light　of　this,　we　carried　out　the　experimental　research　described　in　this　paper.　First,　based　on　a　theoretical　analysis,　a　narrow-linewidth　linearly　polarized　pulsed　fiber　laser　system　was　designed;　then,　an　experimental　platform　of　a　multistage　master-oscillator　power　amplifier　(MOPA)　structure　was　constructed,　including　one-stage　continuous　optical　amplification　and　four-stage　pulsed　optical　amplification.　In　our　experiments,　without　phase　modulation,　a　linearly　polarized　narrow-linewidth　fiber　laser　achieved　an　average　power　output　of　17　W　and　a　peak　power　of　188　kW　(repetition　frequency　of　10　kHz,　pulse　width　of　8.5　ns).　At　this　level　of　power,　the　spectral　signal-to-noise　ratio　was　about　40　dB,　and　the　beam　transmission　factors　in　the　X　and　Y　directions　were　1.14　and　1.11,　respectively.　Using　PRBS　phase　modulation,　a　linearly　polarized　narrow-linewidth　pulsed　laser　achieved　an　average　power　output　of　30　W　and　a　peak　power　of　376　kW　(repetition　frequency　of　10　kHz,　pulse　width　of　7.5　ns)　at　a　clock　rate　of　1.25　GHz.　The　polarization　extinction　ratio　was　greater　than　15　dB,　the　spectral　signal-to-noise　ratio　was　greater　than　40　dB,　and　the　beam　transmission　factors　in　the　X　and　Y　directions　were　1.18　and　1.12,　respectively.