A method to characterize the retardance of retardation films at different wavelengths was presented. Based on a 1/4 λ wave-plate rotation method,the system used a spectrometer as the light source,color filters and a photodetector. Some samples were measured using the system,and the characteristic spectra of the retardation films were obtained by analysing the measurement data.The obtained spectral data show that the blue light retardation is (1-3.5%) that of the green retardation and the red light retardation is (1+2.6%) that of the green one. These results indicate that the dispersion effect of retardation films are not obvious,and the retardation characteristics of different retarders generated by the same material are almost the same,which would be useful to study how the color liquid crystal display is affected by dispersion effects of retardation films. Because the variation of the light source and other errors related to light intensity are not so critical for the measurement in this system and some 1/4λ wave-plates affect on the other wavelengths is very little, the retardance can be measured in high accuracy and high repeatability. In principles,the system accuracy can measure any retardance ,and can be used in characteristic spectrum analysis of other phase retarders.