We propose a modified snapshot spectroscopic ellipsometry based on optical frequency-domain interferometry. The proposed system employs only one high-order retarder and a Wollaston prism to analyze the changed state of polarization of the reflected light and can provide the maximum channel bandwidth of the channeled spectroscopic ellipsometry. The spectroscopic ellipsometric parameters of isotropic samples can be accurately measured in a measurement speed of 40 ms without mechanical or active modulation devices. The feasibility of the proposed spectroscopic ellipsometry is demonstrated by experiments. © 2020