Photogenerated carrier relaxation process and terahertz conductivity of Cd _0.96Zn _0.04Te are investigated by optical pump-terahertz probe spectroscopy at room temperature. With photoexcitation at 800 nm, the photogenerated carrier recovery process can be fitted with a single exponential curve, and its recovery time lasts several nanoseconds, which decreases with the increase of photogenerated carrier densities in a certain range of photogenerated carrier densities, relating to the radiative recombination of electron-hole pairs. The transient transmittance change of terahertz pulse remains the same with the photogenerated carrier densities increasing from 4.51×10 ¹⁶cm ^–3to 1.81×10 ¹⁷cm ^–3, which is because the number of loss carriers by defect trapping is approximate to the augment of carriers by photoexcitation. As the photogenerated carrier density increases from 1.81×10 ¹⁷cm ^–3to 1.44×10 ¹⁸cm ^–3, the magnitude of photoinduced absorption increases linearly with the increase of photogenerated carrier density due to the fact that most of the defects are occupied. When the photogenerated carrier densities are higher than 1.44×10 ¹⁸cm ^–3, the magnitude of photoinduced absorption remains almost the same, because the absorption of 800 nm pump pulse reaches a saturation level. The evolution of complex conductivity with photogenerated carrier density in a delay time of about 50 ps can be well fitted with Drude-Smith model. Our analysis provides an important data support and theoretical basis for designing and fabricating of Cd _1–xZn _xTe detection.