Abstract: This paper consists of two parts,namely,theoretical bases and numerical analysis.In the first part,it has been proved by using a multilevel primitive equation model that if the atmospheric motion 6e symmetric at the initial instant to in the case of symmetric orography,then the motion would be kept in the symmetric state at any instant t>to, This also has been verified by numerical experiments in the second part. Therefore,it can be used as the base of analysing the reasonableness of the dynamic frame of a multilevel primitive equation model.However,if real orography is considered,the symmetry of the atmospheric motion would much be reduced.The main areas affected are the highlands in the Northern Hemisphere and the lowlands at the same latitudes of those highlands in the Southern Hemisphere, Furthermore,such reduction is gradually propagated from low level to high level.