In this paper, we proposed a novel ultra-flat broadband microwave frequency comb (MFC) generation based on optical frequency comb (OFC) with a multiplequantum- well electro-absorption modulator (MQW-EAM) in critical state. The scheme is simple and easy to adjust. The performance of the MFC generation scheme is investigated using software Optisystem. The results show that the comb spacing of MFC can be adjusted from 5 to 20 GHz by changing RF signal’s frequency and the MFC is almost independent on the linewidth of the tunable laser diode. The performance of the MFC can be improved by reasonably increasing the voltage of the RF, the smallsignal gain of the Erbium-doped fiber amplifier (EDFA) and the responsivity of the photodetector. The MFC generated by this scheme has 300 GHz effective bandwidth with 15 comb lines, whose power variation is 0.02 dB, when the components’ parameters in the Optisystem are set as follows: the power of tunable laser diode (TLD) is 0 dBm, the wavelength is 1552.52 nm, and linewidth is 1 MHz; RF signal’s frequency is 20 GHz and the voltage is 10 V; the reverse bias voltage of MQW-EAM is 6.92 V; the small-signal gain of the EDFA is 40 dB; the responsivity of the photodetector (PD) is 1 A/W.