The extraordinary floodinducing rainfall in South China in June 2005 is analyzed synoptically on the basis of the conventional observation data and NCEP/NCAR reanalysis data. The results show that the heavy rainfall, which had two main rain belts and significant daily variations, was mainly associated with the active 500 hPa trough, 850 hPa shear line, lowlevel jet and crossequatorial flows. The westerly fluctuations related to the 500 hPa trough and 850 hPa shear line (tropical systems related to the strong southwesterly and crossequatorial flows) mostly account for the rain belt in the northern (southern) part of Guangdong province. As the activities of the westerly fluctuations decayed, the north rain belt decreased gradually. The southern rain belt had the peak periods of rainfall corresponding to the peak phrases of the meridional winds in the midlow layer over the southern coastal area, which indicates the impacts of the lowlevel jet. The occurring of heavy rainfall was induced by the strong cross equatorial flows, which provide sufficient water vapor for South China, and the end of heavy rainfall is featured by the buildup of the upperlevel easterly.