With the limit of photo-sensitization,when the channel number becomes large,it's unrealistic to fabricate such sampled fiber Bragg gratings(FBG). Phase-only sampled FBGs were demonstrated to effectively reduce the maximum refractive index modulation(MRIM). A hybrid method which employs the inverse scattering(IS)technique and the optimization strategy is demonstrated to be efficient for the design of multi-channel fiber Bragg gratings. Optimized by genetic algorithm(GA),a set of optimal constant phases are introduced to the phase responses of the multiple channels,which lead to a modified complex reflection spectrum of the multi-channel fiber Bragg grating. Then,the layer-peeling IS algorithm is applied to extract the grating index profile from the modified spectral response. By introducing a set of optimal phases to the phase response of the multiple channels,the target reflection response of the multi-channel FBG is modified,which ensures the MRIM of the N channel grating is about only √N times that of the single channel grating. The simulation results show that this hybrid method reduces the MRIM required for 8 channels to approximate √8 times that of the single channel.