The diffraction grating, as an element that can control the direction of the emitted light, is the key component used in holographic sampling three-dimensional (3D) displays. The structural accuracy of nanogratings greatly affects the precision of light modulation, thus influencing the cross talk and resolution in 3D displays. It is of great significance for the nondestructive measurement of nanogratings. However, existing measurement methods have certain limitations such as destructiveness and low measurement efficiency in the face of measuring such pixelated nanogratings. In this work, aimed at the measurement requirements and challenges of pixelated nanogratings in 3D displays, we propose to use a self-designed imaging Mueller matrix ellipsometer (IMME) for grating characterization. A sample containing 6 periods and 10 orientations of pixelated gratings is investigated to verify the effectiveness of the method used. Through the measurement and fitting data, the measurement data obtained by using the IMME can be well matched with the theoretical results. At the same time, the extraction results of the structural parameters, periods, and orientations are also consistent with the measurement results from scanning electron microscopy. It is expected that the IMME will provide a guarantee for the accurate display of 3D holography.