Abstract: Small-scale ripples in intense laser beams caused by intensity or phase modulations will grow fast due to self-focusing effect after passing through the nonlinear media. This lead to the change of the intensity distribution in the beam and can cause media damage by filamentations when the nonlinear phase retardation(B integral) reach to the restriction value which partly depends on the primary ripple level. The certain D B restriction of laser system was obtained by numerical simulations which were coincidence with experiments on beam propagation in a rod Nd3+:glass.