Cascaded coupler interleaver using optical lattice FIR filter model in z-transform is theoretically analyzed. Programming based on the algorithm to resolve optical lattice array concrete parameter （unit time delay △T and coupler angle θk） for objective function, corresponding relationship between z domain low-pass filter with about 0.5 boundary normalized frequency for pass band and optical domain interleaver are discussed. Five kinds of filters （from a to e） are designed, with rectangle-like amplitude frequency response characteristic curve, fiat top pass band, nearly 0 dB ripples, and isolation up to 50 dB.