By　changing　the　fiber　coil　radius　of　F-P　cavity　all-fiber　laser,　the　output　power　of　the　laser　in　the　cladding　and　the　beam　quality　were　studied.　A　hundreds-watts　class　all-fiber　laser　with　the　output　power　of　300W　and　wavelength　of　1　080　nm　was　build　when　the　maximum　pump　power　was　436　W.　The　beam　quality　was　tested　of　M2=1.13　and　optical-optical　conversion　efficiency　was　69%.　The　radial　power　distribution　of　the　fiber　guided　wave　modes　in　20/400　μm　large　mode　area　double-clad　fiber　was　analyzed.　Also　the　fiber　bend　loss　of　two　guided　wave　modes　LP01　and　LP11　was　calculated.　By　fiber　bending　mode　selection　method,　the　fiber　bending　impact　on　the　beam　quality　was　theoretically　and　experimentally　studied.　It　is　found　that,　fiber　bending　mode　can　effectively　eliminate　high-order　guided　wave　mode　LP11　and　a　better　beam　quality　factor　M2=1.06　is　obtained　through　stripping　the　light　in　fiber　clad　after　fiber　bending.　©,　2014,　Chinese　Society　of　Astronautics.　All　right　reserved.