A scanning white-light interferometer is built for precisely measuring phase properties of dispersive multilayer thin film structure with the aid of the commercial spectrometer. Combining seeking optimal function for interferogram maximas with wavelet denoising algorithm, a novel time-domain algorithm is presented which enables the direct extraction of group delay and thus obtains a remarkable decrease of noise level in group delay and group delay dispersion. The apparatus shows reasonable potential for multilayer measurement, material characterization, displacement measurement as well as profilometry.