Abstract: A case of mei-yu front with heavy rainfall in the Changjiang and Huaihe River valley is studied in this paper. By calculating the deformation field, divergence and their corresponding terms of frontogenesis functions, their roles on the maintenace of the front and the development of frontal turbulence are analyzed. The unstable low level jet on the south side of the front is investigated. And, a special dynamic role resulting from its coupling with upper level flow, which would construct a specific secondary circulation, is also studied.