Abstract: ECMWF/WMO 2. 5°×2. 5° grid data are used to compose 12 processes of extension and return of the West Pacific Subtropical High for the summer months from 1980 through 1983. The composite fields are used to compute the condensation heating rate for East Asia and discuss its distribution and medium-range fluctuation patterns,and their relationship with the processes of extension and return of the West Pacific Subtropical High. It is shown that the fluctuation of condensation heating over the eastern Mainland China, caused by the influx of the tropical southwesterly monsoon, is the most immediate driving force for the processes of extension and return of the subtropical high, which are true reflection on mutual influence and restriction between the heating fields of the region and integral constituents of the East Asia mdnsoon circulation system in a two-way feedback.