Abstract: From the idea of stimulated light scattering, the coupling-waves equations of two-modes scattering for Laser propagation in the atmosphere is derived in this paper. On the condition of frequence shift of scattered light (acoustic wave frequence) equals zero (ω=0). these equations reduce to the corresponding equations in Karr's literature [1]. The fundamental pictures for small-scale instabilities induced by STRS of HEL propagation in the atmosphere are obtained using numerical simulation 4D program. The results are similar to that of transversal spacing being infinit in [1].