In this talk, we present our recent work on tuning the polarization states of light wave with 2D or 3D metastructures. First, we illustrate an approach to tune the phase difference of light via time retardation in a microstructured surface. Second, we demonstrate a general mechanism to construct the dispersion-free metastructure. Third, we present a freely tunable polarization rotator for broadband terahertz waves using a metastructure, and also an example on dynamically-switching the polarization state based on the phase transition of vanadium dioxide. The investigations provide some guidelines to control the polarization state of light at subwavelength scale.