Improvement of the nonlinear optical properties, mainly photoinduced enhancement of effective second harmonic generation was observed in Bi3TeBO9 (BTBO) crystals under irradiation of two external UV laser beams. The effect is caused by an interaction of two coherent photoinducing beams of nitrogen laser with wavelength 371 nm near the Bi3TeBO9 fundamental edge, resulting in formation of additional anisotropy. To explain the observed phenomenon and establish the general features of the electronic structure, the band structure calculations, as well as electronic density of states, elastic properties and principal optical functions were simulated by means of the density functional theory approach. The comparison of the nonlinear optical properties with the conventional alpha-BIBO crystal shows that BTBO is a promising material for the fabrication of UV laser optical triggers.