A miniature extracavity terahertz(THz) parametric oscillator is proposed based on surface-emitted technology. Using a small sized pulsed laser to pump MgO:LiNbO3 crystal, the THz-wave is emitted perpendicularly to the crystal surface by optimization design of three-wave non-collinear phase-matching optical parametric oscillation structure. This configuration can reduce the absorption of the THz-wave and improve the beam quality. The THz-wave can be tuned from 0.69 THz to 3.01 THz. When the pump energy is 128 mJ, the maximum average power of the THz-wave is 10.8 W at 1.6 THz , corresponding to an energy conversion efficiency of 8.4310-6. This room-temperature-operated, miniature system is suited to a variety of applications such as spectral analysis and THz communications.