Abstract: In this paper the dynamic mechanisms of the subtropical planetary quasi-stationary vortices in upper troposphere, such as the South Asian high and the ocean thoughs are studied by using a highly truncated, baroclinic spectral model, in which the thermal forcing and the nonlinear interaction between zonal flow and waves, as well as the basic zonal wind changing with latitudes are incorporated. It is revealed that there is a sort of equilibrium state in which stability and features of upper flow field might reflect the main characteristics of the vortices. The control effects of thermal forcing are also discussed.