Abstract: In the stratified atmosphere in which the moment nondivergent approximation was applied, the nonlinear term was introduced because of the nonhomogeneous spatial distribution of density. The solution to be of the form of progressive wave is considered and obtained a two-order nonlinear equation. By means of this system, all results which were derived by Liu Shikuo(1984) were obtained.Moreover, it can be proved that there existed periodic solution in the nonlinear system when there existed periodic solution in the one-order approximation system, and some mathematic problems that were caused by using series expansion were linear system is avoided. In this paper, a series of approximatic solution of nonalso discussed.