In this paper,two schemes are studied to generate flat wide comb base d on two-sided band modulation,which are cascaded two intensity modulators (MZ M ) or cascaded MZM and phase modulators (PM).The relationship between modulation voltage and bias voltage is obtained by theoretical analysis.On this basis,we discuss the influence of high-order sideband and phase deflection on the flatn e ss of the two schemes.If the two schemes want to achieve the same flatness,the output bandwidth of cascaded MZM can be as high as 500GHz,which is wider than that of cascaded MZM and PM;if the two schemes have the same output comb bandwi dth (300 GHz),the flatness of cascaded MZM can reach 0.2db,while the flatness o f cascaded MZM and PM system is only 2.1dB,so the two intensity modulators can produce The raw wide comb has better performance in comb flatness.This provides a solution for the generation of flat comb and the flexible use of modulator.