Terahertz (THz) time-domain spectroscopy (THz-TDS) has been widely applied due to its unique ability to simultaneously measure the refractive indices and absorption coefficients of various materials in the THz region [1–3]. However, traditional THz-TDS fails to detect directly polarization information, so it cannot be used to sample directly the polarization-related properties, such as magneto-optical effect [4,5], birefringence and complex permittivity [1,6], chiral molecular identification [7], and polarization imaging [8,9]. Despite this, through traditional THz-TDS, THz polarization information can still be characterized by multiple measurements with different orientations of the THz polarizer or electro-optical (EO) crystal used [1–3,8]. By inducing time delays to cascade the THz-TDS of the THz orthogonal components [10,11], THz-TDS by electro-optical sampling (EOS) with birefringent crystals can carry out the THz polarization detection with a single scan. Some other developments have also been made to detect the THz orthogonal components, simultaneously, e.g., setting two arms for orthogonal detection in THz-TDS by EOS [12,13], adding periodic modulation of the probes through rotating the EO crystals or the polarizers continuously [14–18], as well as adopting special photoconductive antenna detectors with three contacts or four contacts [19–21]. However, all above need pump-probe scans for one or more times, so excellent repetition is required for their targets, and the detections are vulnerable to the disturbances from the fluctuations of the detection systems and environments. In recent years, some methods have been made to realize single-shot THz-TDS [22–24], which can avoid the detections from the time-consuming pump-probe scans and the requirement of repeatability. Unfortunately, all the single-shot setups are not able to work directly well for THz polarization characterization. Consequently, we focus on the design to realize effectively single-shot THz polarization detection (SS-THz-PD) based on THz-TDS by EOS. It can simultaneously detect the horizontal and vertical components of THz-TDS based on THz phase modulations without the need for an optical scan; thus, it can work with high effectivity and high quality.