Abstract: A diagnostic study of the dynamic and thermodynamic structures of Meiyu fronts in 1—10 June, 12—28 June, and 20—30 July 1998 is presented. It is found that fronts affecting precipitation over South China in early summer have the same dynamic and thermodynamic structures as Meiyu fronts over the Yangtze River Basin. They have the same structural characteristics as tropical synoptic systems. The vertical dynamic and thermodynamic structure of Meiyu fronts has quasi-tropical characteristics, the transition between ITCZ and the extra-tropical front.