In the single-mode fiber,the cascaded symmetric slow taper was pulled out and t he structure of Mach-Zehnder interferometer (MZI),which was put into the optical fiber loop mirror.The improvement of the filter characteristics of the new-kind MZI is stu died experimentally.The transmission spectrum of loop mirror filter is formed by the noncoherent su perposition of MZI and Sagnac interference,and the tunable filter ca n be realized by tuning the new type MZI.The experimental results show that the filter can improve the characteristics of the comb filter in the range of free spectrum within 60nm (1425－ 1485nm),and the tunable filter can be realized.The output waveform of the structure is stable,the modulation depth is greater than 20dB,and the filterin g characteristics of the fiber loop mirror are optimized.