The characteristics of mesoscale convection systems(MCS) associated with t he remnant of the downgraded severe tropical storm Bilis are studied using vario us kinds of observation data and numerical simulation. During Bilis’s going int o inland of southern part of China, the MCS developed quickly and kept active du e to the maintenance of southwest monsoon. A high resolution simulation by ARPS model gave almost the same rainfall patterns with the observation. Analysis was carried out using modeling data for studying the 3dimension structure and evol ution of the MCS. During the downgrading process of Bilis, obvious baroclinic st ructure generated, and the secondary circulation induced by vertical shear of en vironment flow determined the MCS activities. The moist 〖WTHX〗Q〖WTBZ〗 vector was also applied for the research of vertical motion of Bilis. MCS in the southern Hunan Province almost developed in north of horizontal wind shear line, which was under constrains of the low level convective instability conditi ons and northerly jet convergence.