An　Ytterbium-doped　double-cladding　fiber　laser　is　demonstrated.　The　threshold　of　the　pump　power　is　about　1.1W.　The　maximum　output　power　is　9.9W　at　the　wavelength　of　1045nm　when　the　pump　power　is　15.3W.　The　slope　efficiency　is　around　70%.　We　discuss　an　exact　numerical　model,　with　a　shooting　method　to　solve　the　power　steady-state　equations.　Numerical　results　about　the　output　power　as　a　function　of　the　pump　power　are　in　good　agreement　with　measurements.