In this study, the high-energy terahertz-wave pulses were generated using a potassium titanyl phosphate (KTiOPO4, KTP) crystal and an experimental scheme that combines a Stokes parametric oscillator and a Stokes parametric amplifier involving the vertical surface emission of terahertz waves. The pump source was a Q-switched laser with an output wavelength of 1064.2 nm, a pulse width of 7.5 ns, and a pulse repetition rate of 1 Hz. The Stokes light wavelength is 1086.2 nm, the angle between the pump and Stokes beams is 4.4°, and the terahertz wave frequency is 5.7 THz. The time-delay device on the pump-light path can ensure that the pump light pulse has a good time coincidence with the Stokes light pulse to be amplified. When the pump light pulse energy is 770 mJ and the Stokes light pulse energy to be amplified is 16.8 mJ, the amplified Stokes light pulse energy is 185.4 mJ and the maximum terahertz wave pulse energy is 6.4 μJ.