To provide reference for rainstorm forecast, two torrential rain cases happened in the western Guangdong Province are diagnosed on the basis of NCEP/NCAR reanalysis data and observational data. The results indicate: Both of the two processes happened at a favorable circulation background, integrating with rich water vapor, strong vertical ascending motion， and unstable atmosphere stratification. The rainstorm area corresponded well with the negative center of vapor flux divergence, the highvalue area and the denseisoline zone of 〖WTBX〗θ〖WTBZ〗se  at 850 hPa, and the highvalue centers of the vertical helicity and the vertical velocity. The storm intensity also matched quite well with the physical quantities in the two rains.