By amdyzing tile resutts of the numerical sinlulations ol nonlinear propagation of three Gaussian gravlly-wave packms in isothermal atmosphere individually, tile nonlinear effects on the characteristics of glavity waves are studied quantitatively. The analyses show that during the nonlinear propagation of gravity wave packets the mean fows are accelerated and the vertical wavelengths show clear reduction due to non-linearity 011 the other band, though nonlinear effects exist, the time variations of the fi'equencies of gravity wuve packets are close to those derived from the dispersion relation and the amplitude and phase relations of wave-associated disturbance components are consistent with the pledictions of the polarization rchttion of giavity waves. This indicates that the dispersion and polarization rehltions based on the linear grawty wave theory can be applied extensively in the nonlinear region