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In terms of Kuo-Qianp-sigma incorporated coordinate five-level primitive equation spheric band (70°N–30°S) model with the Ural high’s effect introduced into it as initial and boundary conditions, study is made of the high’s influence on Asian summer monsoon circulation and dryness/wetness of eastern China based on case contrast and control experiments. Rusults show that as an excitation source, the blocking high produces a SE–NW stationary wavetrain with its upper-air atnicyclonic divergent circulation (just over a lower-level trough zone) precisely over the middle to lower reaches of the Changjiang River, enhancing East Asian westerly jet, a situation that contributes to perturbation growth, causing an additional secondary meridional circulation at the jet entrance, which intensifies the updraft in the monsoon area. As such, the high’s presence and its excited steady wavetrain represent the large-scale key factors and acting mechanisms for the rainstorm over the Changjiang-Huaihe River catchment in the eastern part of the land.