Abstract: 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 300 W 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 m 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.