Abstract: In order to realize the monomode output in large core multimode double-clad fiber laser to suppress the nonlinear effects in high power double-clad fiber lasers,mode selection by bending the large core multimode double-clad fiber to a suitable radius was used.Theoretical analysis and experiments about mode selection in large core multimode double-clad fiber laser were demonstrated in this paper.Factors that influence the laser bending loss and output mode,such as inner-clad refractive index,core radius,laser wavelength,bending radius,were obtained.Monomode output was obtained from multimode double-clad fiber laser by bending the homemade Yb3+-doped large core multimode fiber.The laser has a fundamental mode output with power of 9W,conversion efficiency of 17.3%.The research is useful in mode selection from large core multimode double-clad fiber laser.