Based on the NCEP/NCAR reanalysis data, conventional observation data, Doppler radar data, meteorological satellite data and ground lightning observation data, the synoptic causes and the mesoscale weather system characteristics of a severe convective rainstorm which occurred in Yunnan on 6 June 2014 are investigated. The results indicate that the forward-tilted trough at 500 hPa, the shear line at 700 hPa and the ground cold front were the crucial synoptic scale systems in this case. High energy and high humidity convective unstable stratification, and obviously vertical wind direction shear were the favorable conditions for the formation of severe convective weather. Many meso-β scale convective systems occurred and developed in the Q vector convergence field. Short-time heavy rainfall often appears around the area with the densest black body temperature (TBB) contour by the side of meso-β scale convective systems moving direction. The variation of rainfall intensity is closely related to the variation of TBB contour gradient. By analyzing the Doppler radar and ground lightning data, we found that meso-γ scale convective system was the direct influence system for the severe convective rainstorm in this case. Thunderstorm usually occurs in area where the echo intensity is between 35-45 dBz and the echo height is more than 10 km. The mesoscale convergence line and the densest negative lightning flash area near the second kind of meso-γ scale convergence zone correspond to short-time heavy rainfall and thunderstorm weather.