Abstract: Based on an invariant of semi-potential vorticity,the scale criterion of geost rophic adaptation in tropical baroclinic at mosphere is discussed.For a deep system,nomatter how long the meridional character istic scale of initial dist urbance is,if the zonal charact eristic scale of initial disturbance is bigger than the equatorial Rossby radius of deformation,the pressure field changes greatly and the zonal current is almost no any change.For a shallo wsystem,when the zonal and meridional charact eristic scales of initial disturbance are greater than the equatorial Rossby radius of deformation,the pressure field is easy to preserve,the zonal current changes to adapt the pressure field,but when the initial disturbance exhibits zonal-type character,the pressure field adapts to the zonal current.