A heavy rain process over the Huaihe Valley during 29 June-2 July 2003 was studied to analyze the thermodynamic and dynamic features of Meiyu front. The following are some conclusions: (1) The event happened under "double blocking" Meiyu synoptic situation, dynamic and thermodynamic structure of the Meiyu front continuously changed. Generally, Meiyu front shows a feature of baroclinicity, but sometimes the front is almost vertical with an apparent quasi barotropy feature. (2)The moisture and energy provided by the convergence and upward motion of the strong southwestern warm and moist air current were responsible for the strengthening and maintaining of the Meiyu front. The heavy precipitation area was located in the strong gradient region north to the maximum of moisture flux.