Abstract: By analyzing the numerical results of nonlinear propagation of a Gaussiangravity-wave-packet in isothermal atmosphere, the effects of nonlinearity on thecharacteristics of gravity waves are studied quantitatively. The analyses show that:during the nonlinear propagation of gravity-wave--packet, affected by nonlinearity,the vertical wavelength show a decrease and the mean flow show clear enhancement.On the other hand, though there exists nonlinear effects, the linear dispersion relation and polarization are still feasible, which indicates that the dispersion relationand polarization based on linear gravity wave theory can be applied extensively innonlinear cases.