In the present work has been presented the results of investigation of the temperature behavior of scattering of light by technological importance nonlinear crystal of barium sodium niobate in wide range of temperature (20-800°C). The complex pattern of light scattering was discovered on the screen in far field near the ferroelectric phase transition (550°C). It was discovered analogy with behavior of light scattering in range of incommensurately phase near 300°, which has been discovered at structural studies (from literature data). On this basis the range near ferroelectric phase transition is new incommensurately phase.