Abstract: A for mula for measuring the baroclinicity of the at mosphere has been defined in this paper. By using the observational data, the relationships between the baroclinic mode of the atmosphere and the spacial structure and time evolution of A sian summer monsoon have been investigated. It is pointed out that there exista strong baroclinic component in wind field during summer time. The time variations of the intensity of baroclinicity in zonal wind are in keeping with the timet able of the movement sof monsoon. The area where the baro clinic wind is stronger can be used to det ermine the monsoon region basically. The horizontal distribution of baro clinicity of meridional wind component and the zonal propagation of baroclinic disturbances in time-longitude cross section are both related to subsystems of the Asian summer monso on regimes.