The single microring resonator was applied to ordinary Mach-Zehnder interferometer filter constituting a new type filter. The output transfer function was derived by the signal flow graph method, and the output spectra were simulated and analyzed. The results show that the improved filter can give rectangular waves approximating flat top and flat bottom, The free spectral range up to 111 GHz, the extinction ratio of 10.2dB. Compared with Mach-Zehnder interferometer filter, free spectral range, the extinction ratio, precision are improved obviously. By changing the way of combination of micro ring resonator and Mach-Zehnder interferometer filter, more output waveforms were got. The effects of various parameters on the output performance of the device was discussed.