Stimulated polariton scattering (SPS) based on noncollinear phase matching scheme from the A₁-symmetry modes of KNbO₃ crystal is investigated for generating terahertz (THz) wave. Frequency tuning characteristics of THz wave by varying the phase matching angle and pump wavelength are analyzed. The expression of the effective parametric gain length under the noncollinear phase matching condition is deduced. Parametric gain and absorption characteristics of THz wave in KNbO₃ are theoretically simulated. The characteristics of KNbO₃ for parametric oscillator (TPO) are compared with those of MgO:LiNbO₃. The analysis results indicate that KNbO₃ is an excellent optical crystal for TPO to enhance the output of THz wave.