Abstract: Based on the conventional observational data,satellite images,retrieval data of radar echo,automatic observational precipitation and NCEP/NCAR reanalysis data,the mesoscale features of an excessive rainfall triggered by low-vortex shear in the western part of South China on 12-13 June 2007 were analyzed.The major conclusions are as follow:(1) the conventional observational data analysis indicated that the rainstorm event occurred under favorite synoptic conditions, which was closely related with activities of some synoptic systems, including the upper-level trough at 500 hPa east of Tibet Plateau being enlarged longitudinally and moving quickly southeastwards,the low vortex at 850 hPa moving eastwards along the shear line,the developing of the southwest jet on lower levels,and shallow cold air movement on the ground with their interaction causing a favorable circulation and motivating the mesoscale convective system development;(2) in the whole process of rainstorm event, the surface rainfall obviously showed meso-scale spatial and temporal distribution features with the horizontal scale of precipitation centers less than 200 km and the duration of approximate 5-7 hours which is distinguished from meso-cale features;(3)the mesoscale convective system invasion was the pivotal cause of the severe torrential rainstorm:the center of the severe torrential rainstorm in Liujiang was composed of two developing MCS clusters, one of them generated in afternoon and moved northeastwards to the place over the rainstorm center along the southwest air flow,and the another cluster occured on the western side of the shear line and moved eastwards to the place over the rainstorm center along the shear line, but the rainstorm center in the coastal area was triggered and developed by a single MCS cloud cluster;the precipitation emerged mainly in the central cloud cluster area or edge of MCS with the cloud brightness temperature less than -52 ℃ and the black boby temperature (TBB) gradient maximized; corresponding to the genesis and dissipation of MCS cloud cluster, the Liujiang torrential rainfall consisted of two meso-scale precipitation processes:the first precipitation process was mainly induced by thermal convective cloud clusters,and the second precipitation process involved mainly severe torrential rains caused by the meso-scale convective systems associated with the lowvortex cloud systems,and,on the other hand,the coastal rainstorm was a shortdurational consecutive event generated by meso-cale convective systems;rainstorms were primarily triggered by developing convective cells emerging in the zone of strong radar echo with the evolution of the VWP products proving that the severe precipitation was generated with the builtup of low level jet (LLJ) stream and the LLJ velocity pulsation at 2-3　km level enhanced the development of the mesoscale convective system; (4)the severe torrential rainstorm occured in the high pseudoequivalent potential temperature tongue featured with high temperature and moisture,where the moisture depth extended above 400 hPa with the rainfall area showed a distinguishable potential instability;（5）MCS had a deep vertical circulation structure with the vortexcylinder at low levels uplifted obviously during precipitation and the water vapor and energy convergence was strengthened;at the same time, the ascending movement caused by dynamic forcing at the frontal zone enhanced upward energy and water vapor transferring from lower levels, and thus the divergence flow was reinforced at upper levels, which all contributed to enhancement of MCS development and generated torrential rainfall; in addition, the trumpetshaped terrain of Guangxi favoured uplifting the stream and reinforced the ascending movement forced by the cold front at the rainfall center.