Some dynamic constrains in the process of the tropical baroclinic geostrophic adjustment are discussed. The dispersion equation of three-dimensional inertia-gravitational wave and the equation of temporal conservation of potential vorticity are given, without considering the gradient of planetary potential vorticity. It indicates that the motions will be horizontal, meaning that Taylor-Proudman theorem is still right for tropics. At the same time, the semi-geostrophic balance is easier to appear in the tropical belt. Therefore the motions are generally horizontal and non-divergent, but still are stratified after the geostrophic balance establishes.