In this article, method for determining in real time the frequency characteristics (amplitude, frequency, and etc.) of mechanical constructions subjected to dynamic loads is presented. This method is based on the analysis of the behavior of the intensity of a single speckle. The optical scheme in which a simultaneous registration of a standard digital speckle interferogram on the CCDmatrix and the behavior of the intensity distribution in a single speckle with using high-speed point photodetector is presented, that allows to simultaneously determine the shape and amplitude of the resonant vibrations of the mechanical structures in realtime. The results of experimental researches are presented.