In　this　work,　we　employed　gain-managed　nonlinear　amplification　(GMNA)　technology　to　achieve　a　pulse　characterized　by　a　smooth　spectral　profile　and　an　exceptionally　wide　spectral　bandwidth.　Then　this　pulse　was　injected　into　a　chirped　pulse　amplification　(CPA)　system　for　amplification,　and　a　high　energy,　narrow　pulse　duration　fiber　laser　system　was　successfully　built.　The　initial　seed　source　for　system　was　a　self-made　mode-locked　fiber　oscillator　that　utilized　a　nonlinear　amplifying　loop　mirror　(NALM).　This　oscillator　produced　ultrashort　pulses　with　a　pulse　duration　of　10.96　ps　at　a　repetition　rate　of　11.52　MHz.　The　spectral　width　of　the　mode-locked　oscillator　was　significantly　broadened　from　5.83　nm　to　63.97　nm　using　GMNA　technology.　Furthermore,　the　spectral　profile,　which　initially　exhibited　severe　oscillation　structures,　was　reshaped　into　a　smooth　profile　through　the　application　of　GMNA.　Subsequently,　the　pulse　energy　was　increased　through　CPA　amplification.　Finally,　in　the　case　of　a　central　wavelength　of　1064　nm　and　a　repetition　rate　of　500　kHz,　a　pulse　with　an　average　power　of　20.02　W,　a　single　pulse　energy　of　40　μJ,　a　pulse　duration　of　179　fs,　and　a　peak　power　of　224　MW　was　obtained.　This　fiber　laser　system　has　great　prospect　of　application　in　clinical　medicine　and　precision　manufacturing　due　to　its　high　energy　and　ultra-short　pulse　duration.　©　2023　SPIE.