Polarization detection characteristics of the electro-optic crystal ZnTe in the terahertz time-domain spectroscopy (THz-TDS) system are investigated. The differential current associates with three factors which are direction of crystal axis, THz polarization direction and probe beam polarization direction. According to theoretical analysis, the differential current is relevant to the angle (α) between the THz polarization and the crystal axis and the angle (φ) between the probe beam polarization and the crystal axis. Experiments and caculations are conducted in the cases of α=φ,α=φ+π/2, α=φ+π/4, and the experimental results agree well with the calculation results.