The whole model of adaptive optics system of energy and information transfer should include a model of an active element [1] construction of which is defined by parameters of the system and beam control algorithm. In the algorithm of full-field phase conjugation a nonlinear crystal or two flexible mirrors with a layer of free space between them are usually employed [2, 3], while a system of phase conjugation requires a flexible mirror as an active element [4]. In the paper the model of a flexible mirror is considered which takes into account dynamic oscillation of reflecting surface.