Based on the theory of four-port resonator filters, the characteristics of four kinds of filters with single race-track, dual race-track, rectangular and MMI resonators respectively were numerically simulated by utilizing two-dimensional FDTD method. The relationship between the number of cascade resonators and the filtering features was also analyzed. A kind of narrow-band filters with four cascade resonators implemented on GaAlAs/GaAs planar lightwave circuits were designed and fabricated. The measurement result shows that the half-width of such filters is about 10nm, which coincides well with the numeric computation. Based on the theory of four-port resonator filters, the characteristics of four kinds of filters with single race-track, dual race-track, rectangular and MMI resonators were were numerically simulated by utilizing two-dimensional FDTD method. The relationship between the number of cascade resonators and the filtering features was also analyzed. A kind of narrow-band filters with four cascade resonators implemented on GaAlAs / GaAs planar lightwave circuits were designed and fabricated. The measurement result shows that the half-width of such filters is about 10 nm , which coincides well with the numeric computation.