High　average　power　linearly-polorized　picosecond　pulsed　laser　sources　have　a　wide　range　of　applications　in　the　fields　of　industrial　material　processing,　coherent　beam　combination　and　nonlinear　optics.　A　high　power　linearly　polarized　picosecond　pulse　ytterbium-doped　all-fiber　laser　based　on　a　seed　of　mode-locked　fiber　laser　with　a　semiconductor　saturable　absorber　mirror　is　reported.　The　fiber　laser　is　constructed　with　a　two-stage　master　oscillator　power　amplifier　(MOPA)　configuration.　Stable　mode-locked　pulse　train　occurs　when　the　incident　pump　power　increasing　and　the　pulse　repetition　rate　is　40　MHz　in　a　ring　cavity　configuration.　Increasing　the　incident　pump　power　to　200　mW,　the　maximum　output　average　power　is　12　mW.　The　pulse　width　is　measured　to　be　20　ps.　The　center　wavelength　and　the　spectrum　bandwidth　are　1038.2　nm　and　1.7　nm,　respectively.　The　steep　edge　in　the　optical　spectrum　is　a　clear　indication　of　the　dissipative　solitons　(DSs)　in　this　all-normal-dispersion　mode-locked　fiber　laser.　After　two-stage　fiber　amplifier　with　the　polarization　maintaining　double-cladding　ytterbium-doped　fiber　as　the　gain　medium,　5　W　average　output　power　is　achieved,　corresponding　to　a　single　pulse　energy　of　125　nJ　and　a　peak　power　of　6.25　kW,　respectively.　No　undesirable　nonlinear　processes　such　as　stimulated　Raman　scattering　are　observed.　At　this　high　output　power,　the　spectrum　bandwidth　and　the　pulse　width　are　measured　to　be　3.1　nm　and　20　ps,　respectively,　and　the　polarization　extinction　ratio　is　20　dB.