In order to improve the transmission performance of conventional Mach -Zehnder interferometer (MZI) filter,a novel all-fiber MZI interleaver is proposed and discussed in th is paper.The all-fiber interleaver consists of two 2×2fiber couplers and one 8-shaped fiber ring resonator.Base d on its structure,the output spectrum expression is established and described by using the principle of fiber transmission and the matrix transfer function.The characteristic parameters,such as amplitude flatness,ba ndwidth and channel segregation,are analyzed and optimized.The results of numeri cal simulation indicate that wh en the first length difference of interference arms is as twice as the second or the third length difference of in terference arms,and the coupling coefficients of the couplers are some certain values,it will obtain a uniform fl at-top passband and similar to square output spectrum.The 25dB stopband bandwidth and 0.5dB pa ssband bandwidth are simultaneously remarkably improved,and their values are 26.2GHz and 38.4GHz,wh ich are much wider than those of the conventional MZI.The device has a certain ability to resist the deviatio n,which reduces the difficulty of making it.The influence of transmission loss o n extinction ratio can be effectively reduced.The experimental results agree with the theoretical analysis well.The study may prov ide reference for the fabrication of the apparatus later.