The　angle-polished　side-pump　coupler　is　fabricated　by　fused　splicing　angle-polished　multimode　fibers　and　20/400　mu　m　double-clad　Yb-doped　large　mode　area　fiber　together.　The　coupling　efficiency　of　side-pumped　coupler　for　975　nm　pumping　light　can　reach　up　to　97%,　and　the　leakage　ratio　of　1080　nm　signal　light　is　less　than　2%.　We　analyze　the　performance　of　a　single　side-pumped　coupler　and　also　the　influence　of　the　distribution　of　cascade　stage　couplers　on　the　efficiency　of　fiber　amplifier.　Using　self-developed　side-pumped　couplers,　we　build　a　distributed　side-pumped,　ytterbium-doped　double-clad　all-fiber　master　oscillator　amplifier,　and　an　continuous　and　single　mode　laser　of　1080　nm　wavelength　with　a　303　W　maximum　output　power　is　obtained.　Finally,　increasing　the　number　of　the　side　couplers　to　improve　pump　power,　the　output　power　of　the　amplifier　becomes　higher.