The invention discloses a method for generating a multi-carrier optical signal, and relates to the technical field of optical communication. The method comprises the following steps of: S1, generating four radio-frequency drive signals f11, f12, f21 and f22, wherein the frequency of the f11 and f12 is fm, and the frequency of f21 and f22 is 3fm, so that first order component generated by the f21 and f22 and third order harmonic component generated by the f11 and f12 have opposite symbols, but same amplitude; S2, driving a modulator to modulate a pre-generated seed optical signal with frequency of f0 by utilizing the four radio-frequency drive signals to generate subcarrier optical signals with frequencies of f0+fm and f0+5fm; and S3, circulating the step S2, and modulating the sub-carrier optical signals generated in last circulation and a fifth-order harmonic crosstalk optical signal once again to generate a new subcarrier optical signal so as to obtain N+1 subcarrier optical signals f0, f0+fm,..., f0+Nfm together with the seed optical signal. The invention also discloses a multi-carrier optical signal generation device. According to the method and the device, the multi-carrier optical signals with large number, high output flatness, good stability and high effective optical signal to noise ratio are generated.