An　experimental　research　on　self-phase　modulation　(SPM)　of　high　power　picosecond　pulse　amplifier　was　conducted　by　high-power　all-fiber　picosecond　pulse　fiber　laser　with　an　MOPA　configuration.　The　seed　source　is　a　self-built　fiber　laser　passively　mode-locked　by　semiconductor　saturable　absorber　mirror　(SESAM).　To　avoid　nonlinear　effect,　the　repetition　rate　of　the　seed　pulse　should　be　increased　to　328　MHz　through　a　self-made　repetition　multiplier　before　amplification.　The　amplifier　employed　a　three-level　amplifying　structure　and　finally　received　a　stable　picosecond　pulse　laser　output　with　a　center　wavelength　of　1　066.5　nm,　a　3　dB　spectrum　width　of　2.5　nm,　and　an　average　power　of　91W.　In　the　experiment,　there　was　research　on　change　of　spectrum　caused　by　SPM　in　the　process　of　amplification.　An　analysis　of　the　output　spectrum　of　the　laser　demonstrates　that　with　the　increase　of　power,　the　influence　of　the　initial　chirp　and　the　shape　of　the　pulse　on　the　SPM　effect　of　high　power　fiber　laser　becomes　deepens.　In　the　mean　time,　it　is　also　influenced　by　self-steepening　effect.