In order to improve the transmission performance of all-fiber three-channel interleavers, an all-fiber three-channel interleaver was developed by using a new configuration of dual-8-shaped ring resonator.The ring was composed of a planar 3×3 single mode fiber coupler and two 2×2 fiber couplers and was used as an input device. Furthermore, a regular triangle 3×3 fiber coupler was used as output device. The propagation properties of the three-channel interleaver were studied experimentally and theoretically. Obtained result indicates that the sidelobe level of channel of the proposed device is reduced by more than 24 dB and the crosstalk characteristics, channel isolation, the bandwidth of passband/stopband, the rolloff in transition band and the coupling-coefficient tolerance have been improved greatly in comparison with that of the convention all-fiber three-channel interleaver based on a two-stage cascaded Mach-Zehnder interferometer(TCMZI). This kind of interleaver was fabricated with a fused biconical taper technics in an experiment. The experimental results are in good agreement with the analytical ones and it shows that the measured sidelobe level is about -30 dB and the channel isolation is higher than 30 dB.