Recirculating frequency shifter (RFS) can generate stable multi-carrier, but the carrier-to-noise-ratio (CNR) is limited because noise is accumulated round by round in the recirculation loop structure. A modified RFS with a delay interferometer (DI) is proposed in this paper. The DI can suppress the accumulated noise, and enhance the CNR of multi-carrier. The principle of the generation of high quality multi-carrier based on an RFS with DI is analyzed theoretically. 50 stable carriers with spacing of 10.7 GHz are successfully generated. The flatness of 50 stable carriers is 3 dB, and the CNR is 43 dB which is increased by 3 dB compared with the structure without DI.