When the momentum,energy and circulation of a fluid in a quasi-geostrophic baroclinic two-layer model are specified,the minimum enstrophy solution of the baroclinic fluid is first obtained by the variation method,and is none other than an exact one of nearly steady baroclinic finite-amplitude problems.If the ratio of length to breadth of the channel,the average depth of fluid and the energy are greater than their critical values respectively, and the circulation is of no vertical shear,the exact solution is the finite amplitide baroclinic Rossby waves;otherwise it is the zonal flows.″principle of no-coexistence″is first proposed meaning that all wavenumbers between the barotropic and the baroclinic components of nearly steady finite amplitude Rossby wave in the baroclinic atmosphere are not the same,This indicates that two kinds of nearly steady waves have quite different horizontal and vertical structures,results that agree with observational facts and outcome of numerical experiments.