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To generate a flat optical frequency comb (OFC), a new scheme based on a dual-parallel Mach–Zehnder modulator and a single recirculation frequency shift loop is proposed and analyzed. Compared with the traditional single loop recirculation frequency shift method, the quantity of comb lines is doubled, and the comb flatness is better when the number of cycles is the same. The theoretical analysis model is established, and the simulation results show that a 111-line OFC with frequency spacing of 10 GHz, flatness of 1.32 dB, and optical signal to noise ratio of 27.4 dB can be obtained by adopting the proposed scheme.