Abstract: By means of a nou-dimensional dynamic parameter μ=(Ky)/(fKz),an analysis of the inertio-gravitational wave characteristic is performed for a modified nou-hydrostatic equilibrium model. The frequency spectra, propagation feature and structure of this wave in middle-high and lower latitudes are dispussed and compared. There is a critical wavelength for the instable stratification inertio-gravitational waves with wave length shorter than which are instable, on the other hand, somewhat longer waves of low frequency than which can disperse the energy ahead of its propagation, then excite new waves. It is shown that one must use entire nou-hydrostatic model which contain term in the investigation of local strong convection and of lower latitude mesoscale numerical forecast.