Abstract: Using pentad mean ECMWF and OLR data from April to September of seven year mean 1980-1986,some aspects of the climatology of the summer monsoon have been dealt over the South China Sea(SCS).Some interesting evidences were revealed.First,the onset of the northern SCS summer monsoon on the average is marked by the onset of the east erly and northerly at 200hPa,the abrupt enhancement of westerly at 850hPa,and the formation of the meridional monsoon circulation of the East Asia.A nother abrupt enhancement of the westerly corresponds to the onset of Meiyu in the Yangtze River valley.Two abrupt increases in the temperatures at 850hP aoccur over China continent during early May and early June.Second,at 850hPa,zonal wind and specific humidit y appear with tw o-peak-pattern,and the abrupt increases of the zonal wind correspond well to the increase of the specific humidity.Before the onset of the summer monsoon,the temperature increases wavily,but drops down wavily after the onset.Last,There exist three abrupt changes in distribution of specific humidity in East Asia separately during middle April with the high humid band appearing over the northern SCS,during middle May with high humid band suddenly jumping from the southern SCS to the northern SCS,and during the period from middle June to August,with the high humid band appearing over the Yangtze River valley and disappearing over the southern SCS.The monsoon evolution charact eristics over the northern Bay of Bengal(BOB) much differs from that of the northern SCS,so this means that the SCS and BOB to a certain degree belong to different monsoon system.