Abstract: By using the obser vational data, the relationships between the barotropic mode of the atmosphere and the structure/time evolution of Asian summer monsoon have been investigated. It is pointed out that the subtropic high belt revealled by barotropic mode of air flow in troposphere can only show us that the planetary wind belt moves seaso nally in meridional direction. Something which is associated with Asian summer monsoon and makes us know where the summer monsoon could probablely be is the wavelike disturbance on eastlies of subtuopic high. Both the directions in which the meridional component of barotropic flow in eastlies propagates zonally and the amplitude of meridional wind disturbances are closely related to the subsystems of India and East-Esian monsoon. When summer comes, the baroclinic mode grows rapidly in Asian monsoon area.The main part of total kinetic energy averaged over a whole air column in tropo sphere is the energy of baroclinic motion. In equatorial region beyond the monsoon area, the barotropic mode grows quickly when the summer time is coming in Northern Hemi-sphere.