Based on the multipletype observational data,this paper preliminarily analyses the mesoscale convective systems(MCSs) and weather background producing an extremely heavy rain along the Meiyu front in Hubei and Anhui provinces during 29—30 June 2009,and investigates the multiscale structure features of the Meiyu frontal rainstorm system.Then the mesoscale numerical model WRF with large domain and 9 km horizontal resolution is used to carry out a 3domainnested fine simulation for the heavy rain process.Morlet wavelet transformation is carried out to do spatial bandpassing filter for the model outputs,and the meso〖WTBX〗α,β〖WTB1〗 and 〖WTBX〗γ〖WTB1〗scale systems are separated out,in such a way that the three dimensional spatial dynamic and thermodynamic characteristics of the mesoscale systems with different scales are studied.The results are as follows.The extremely Meiyu frontal heavy rain is directly resulted from several MCSs with different scales,which are of different features on satellite cloud images and radar echoes.On meso〖WTBX〗α,β〖WTB1〗 and 〖WTBX〗γ〖WTB1〗scales,the Meiyu frontal heavy rain system has obvious different dynamic and thermodynamic structure features in horizontal and vertical directions.The meso〖WTBX〗α〖WTB1〗 and 〖WTBX〗β〖WTB1〗scale systems have obvious vertical circulation,while meso〖WTBX〗γ〖WTB1〗scale system has some features of inertial gravity waves and usually develops in meso〖WTBX〗α〖WTB1〗 and 〖WTBX〗β〖WTB1〗scale system.Lastly,a physic conceptual model is advanced for the typical Meiyu frontal rainstorm system.