In the context of May to September 1980～1986 ECMWF dailr 850 hPa data,analysis is mad e of the seasonal mean and low-frequency structures for water transportation in the Asian stimmer monsoon region.Results show that the monsoon system is a complete feature asviewed on a seasonal mean basis,and two relatively independent subsystems(the Indian and East-Asian monsoons)can be identified in the Asian summer monsoon system from the perspective ofthe low-frequency structure.