In order to improve the output performance of all-fiber interleaver, a novel all-fiber Mach-Zehnder interferometer (MZI) interleaver which uses a 2×2 fiber coupler with self-feedback as the output coupler is proposed. An output expression of the system is derived and simulated numerically. The results show that the transmitted waveform of the proposed MZI-Interleaver is close to a square wave, and the rejection in stopband and the rolloff in transition band are improved remarkably. Compared with the traditional MZI-Interleaver based on fiber resonator, the difference between the intensities of two coherent lights dose not exist when the influence of the propagation loss is considered, and the influence of the propagation loss on extinction ratio of all-fiber MZI-Interleaver can be effectively reduced.