The potassium tantalate niobate (KTN) crystal has a high quadratic electro-optic coefficient and a fast response speed; therefore, it can be used to develop a high-speed electro-optic switch, which can quickly achieve a large beam deflection angle at a low voltage. However, the dispersion problem of the KTN crystal limits its application as an electro-optic switch in a wide spectral range. We investigate the effects of control voltage, temperature, and wavelength on the deflection characteristics of the KTN crystal, and find that simultaneous adjustment of voltage and temperature can balance the beam deflection angle and dispersion. This study provides guidance to the application of KTN crystals in wide-waveband beam deflection.