Abstract: In order to generate an ideal output shape, the on-line filtering technology was introduced into fiber Mach-Zehnder interleaver. The sharp edge filtered output of approximating wideband was realized by adding interference orders，adjusting the interference length of the two pairs of interference arms and coupling ratio of the coupler. The coupling ratio should be corrected to improve the output characteristics. By comparison with Fourier function of trapezoid filter, the key parameters of Mach-Zehnder interleaver were worked out. The properties of output and the temp-stability are optimized. A sample component with the channel interval of 50 GHz was made. When its output is -0.5dB, the band width is more than 0.185nm and the interval between the consecutive channels is over 30dB. The theoretical results are consistent with the experimental results and they meet the requirement of DWDM system.