Five cell parameters of a twisted nematic liquid crystal device (TNLCD), namely, cell gap, pretilt angle, twisted angle, rubbing angle, and phase retardation are precisely measured by the developed amplitude-sensitive heterodyne polarimeter (ASHP) simultaneously integrated with Yeh and Gu's transfer matrix and Lien's transfer matrix. This proposed method can characterize the five cell parameters under the arrangement of a single wavelength at normal incidence. In contrast to the conventional methods on cell parameter detection either by adopting a multiple wavelength laser beam at normal incidence or by using a single wavelength laser beam under oblique incident to TNLCD, this method presents the advantage of not only having a simple setup but also the possibility to measure simultaneously five cell parameters on the characterization of TNLCD at high speed.