Abstract: Based on the daily precipitation data of 83 stations in Guangxi and the NCEP/NCAR monthly reanalysis data from 1979 through 2008, the characteristics of spatial and temporal distribution and variation of the rainstorm-concentration degree (RCD) and the rainstorm-concentration period (RCP) are analyzed by using the methods of Monte Carlo test etc. The results are shown as follows. The rainstorm events are concentrated in April-September, taking up about 90% of the yearly total rainfall, and the percentages of rainstorms accounting for the annual total precipitation have an increasing tendency. RCD in the east of Guangxi is larger than that in the west. The RCP in the northeast and southwest of Guangxi is later than that in the other regions, and that in the northern mountainous regions of Baise and southeast Guangxi is the earliest. The RCD exhibits an increasing tendency in the northwest and the coastal region while showing a decreasing tendency in the other regions. On a long-term basis, the RCP in the east and coastal region has a postponing trend and that in the other regions tends to be earlier. The proposed mechanism is as follows: If the geopotential height in the south of Qinghai-Tibet Plateau and the West Pacific has a highly negative anomaly in winter, the western Pacific subtropical high is strong in summer, which will increase RCD in Guangxi; If the geopotential height has a highly positive anomaly in winter, the subtropical high has a significant periodic oscillation in summer, which will increase RCD in Guangxi. The value of RCD is high (low) in the area of northern mountainous regions of Guangxi and Beihai in strong (weak) South China Sea summer monsoon years, while in the other areas, the value of RCD is low (high).