By utilizing the conventional meteorological data, precipitation data of automatic meteorological stations, and NCEP reanalysis data (1°×1°), the process of the severe rainstorm happened in Fujian in early June 2017 is analyzed. Some conclusions are derived from the results: (1) The continuous precipitation was formed by the interaction of the northern cold air flow and the warm and wet flow from the south. The activity of mesoscale systems caused the shortterm rainstorm. (2) Relatively large relative helicity, positive vorticity at the lower level, and rising movement at the middle and low levels were beneficial to the development and maintenance of MCSs. Strong thermal instability and strong vertical wind shear were the ambient characteristics of mesoscale convective development. (3) The strong whole layer vapor flux and water vapor convergence provided water vapor sources and conditions for the rainstorm area. (4)The size and position of the frontogenesis can be exploited as good indicators of the intensity and the falling area of the rainstorm. The lower level was dominated by horizontal frontogenesis and the middlelevel was dominated by vertical frontogenesis, which was beneficial to large areas of heavy rainfall. (5) The mesoscale systems played a role in strengthening synoptic scale water vapor convergence, and meanwhile enhanced the convective instability conditions of the boundary layer. The upper and lower branches of the two secondary circulations were superposed, and this superposition was beneficial to the release of the instability energy accumulated at lower level, and promoted the development of the mesoscale system.