Abstract: A design of large-mode area photonic crystal fiber (LMA-PCF) was proposed to improve the non-linear effect of high-power fiber laser, which has the properties as large effective mode area, single mode, passive component, and low loss. The perfect matched layer was set as the boundary condition, and the effect of wavelength and structure on the effective mode area of PCF were analyzed by the finite difference time domain method. Further, a program of LMA-PCF was proposed. The results indicate that the transmission of single mode is obtained. At the wavelength of 1.064μm, the effective mode area is able to reach 3118.4μm², and the non-linear coefficient is only 5.68×10^-5 m^-1·W^-1. Besides, the confinement loss can be reduced to 4.55×10^-7 dB·m^-1. Therefore, the high-power and high-beam of laser output is realized.