The discrete layer-peeling method for designing multi-channel fiber Bragg grating was optimized. Through the new method, after inserting different phase changes at different channels, the coupling coefficients was then fitted by Gaussian function to get a lower and more smooth refractive index modulation. The simulation results show that a 8-channel fiber Bragg grating is successfully designed using the proposed method with the maximum refractive index modulation of 0.000 5, much lower than that of traditional DLP method (0.001 3), which decreases the requirement of fiber′s optical sensitivity. And, the difficulty of inscribing a fiber grating was reduced by smoothing the refractive index modulation.