An extensive very heavy rain fell over the Huaihe River on August 23 and 24, 1980. It is pointed in this paper that due to the large-scale tropical SW-S-SE monsoon current confluent zone from the Bay of Bengal-South China Sea-NW Pacific, to its north, at the downstream of the confluent point, a South China vortex was introduecd and developed with 7-8 spiral cloud belts. The SW jet stream on lower level intensified and propagated eastward. It not only induced an energy frontal zone between Yangtze and Huaihe Rivers, but also steered the South China vortex moving eastward. At last, a very heavy rain occurred in the warm sector to the southside of the vortex, just over the Huaihe River.