Abstract: The occurrence of the abnormal weather of China in summer 1980 was intimately related with the eruption of Mt.St.Helens in May 1980 which is one of the great volcanic eruptions since 1900.Throwing up to the stratosphere and floating with the Jet,large quantities of volcanic dusts continually circulated around the temperate zone of Northern Hemisphere.Measurement of the direct solar radiation (S) of clear skies from East China north of 30°N has proved that an abnormal lowering of S had commenced since early 3une and dropped down to a minimum for recent 22 summery records,it changed little in the region south of 30° N.Thus,the enhanced meriodinal gradient of the solar heating forced the west Pacific subtropical high and the monsoon rainy belt retreating southward in early July to an abnormal seasonal location during July and August.So,the large scale drought in North China,the great waterlogging in Changjiang and the cold summer prevailing over Changjiang-Nuaihe valleys occurred.