High-power nanosecond pulsed THz-wave radiation is achieved via a surface-emitted THz-wave parametric oscillator.One MgO:LiNbO3 crystal with large volume is used as the gain medium.THz-wave radiation from 1.084 THz to 2.654 THz is obtained.The maximum THz-wave average power is 5.8 μ W at 1.93 THz when the pump energy is 84 m J,corresponding to a energy conversion efficiency of 6.9 × 10-6.The polarization characteristics of THz wave are analyzed.During the experiments the radiations of the first-order and the second-order Stokes wave are observed.The THz wave has great scientific research value and wide applications in imaging,material detection,environmental monitoring,communication,astronomy,life sciences,national defense security and so on.[1-4] THz-wave parametric oscillators (TPOs)based on stimulated polariton scattering have many advantages,such as high efficient,coherent,tuning,narrow linewidth,compactness and room-temperature operation.[5-7] In recent years,TPOs have been developed rapidly.Stothard et al.[8] reported on a line-narrowed and widely tunable intracavity TPO,in which the linewidth of the THz wave is about 1 GHz,the tunning range is from 1 to 3 THz,and the peak power of the THz wave is about 3W.Wu et al.[9]reported on a TPO with recycled pump beam,and their experiment results show that the THz-wave out-put power increases almost four times in magnitude.