An optical test system based on the optical fiber spectrum analyzer is designed and established.A series of two-dimensional periodic-arrays samples with chiral m orphology are fabricated by electron-beam lithography technology.The periods of samples are measured by scanning electro microscope (SEM),which are 520nm,570nm,and 790nm respective ly.On condition that the incident light is pe rpendicular to the surface of the sample,the change rule of the spectrum with diffractio n angle under the white light is tested and analyzed firstly.Meanwhile,the measurement effect on the c ycle length of complex morphology two-dimensional periodic-arrays is tested by diffraction optical me thod.The results indicate that the diffraction spectra of all samples will gradually move to long wavelen gth when the diffraction angle increases.And on the same diffraction angle,there is a relationship be tween the diffraction wavelength and the period length of the sample.Through the derived cross-grati ng diffraction equation, the diffraction spectral change of the sample under the normal incidence is si mulated.The result is satisfied well,which indicates the applicability of cross-grating diffraction e quation in complex morphology structure.Thus the period lengths of the samples are calculated,and we get that the deviation of the results from the observations of SEM is less than 3％.