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.