Abstract: Through the diagnosis of a Meiyu frontheavy rain process occurring from 1 to 3 June,2000,this paper has studied the affection on the rainstorm caused by the ageost rophic wind,the unbalanced flow,low level jet (LLJ),and the generation and propagation of gravity wave after the abrupt change in large-scale circulations.The result sillustrate that the subtropical high suddenly moved northwest ward,then the geostrophic balance was dest royed,local pressure gradient increased rapidly,and unbalanced flowoccurred,thus the adjustment of circu lation was caused so as to build a new balance.During this process,LLJ and gravity wave appeared to meet the change.Unbalanced energy dispersed through the divergence and convergence of the geost rophic departure wind.The gravity wave dispersion canpromote the propagation of the strong wind center along the LLJ,and the dispersion direction was inf luenced by the steering flow and the water vapor concent rated area.The LLJ is one of the import ant conditions to induce heavy rain.Especially in the leftfront part,the convergence and shear of wind occurred.It is fend to the generation of disturbance,meso-vortex,and meso-convective system and provided a favorite condition for the rainfall.Based on the analysis of the high resolution simulating data,all the results can be clearly illustrated.