Abstract: The fluxes of sensible heat and latentheatin the South China Sea(SCS) and its neighboring regions are expanded by means of EOF in this paper based on the reanalyzed data of the SCSMEX from Jan.1 to Aug.31,1998.It is found that there exist three areas with higher values of sensible heatin the Indochina Peninsula,the northeastern Tibetan Plateau and the most part of the Indian Peninsula,whereas the area with lower values is located in the sea,therefore the land-sea thermal contrastis very obvious.It is the background of monsoon onset.The continuous sensible heat distribution from south tonorth within the longitude of Indochina Peninsula makes the monso on firstly onsetin SCS region.The heating effect of the Indochina Peninsula is evidently earlier than that of the Tibetan Plateau,therefore,the Indochina Peninsula has an important function in the early on set of the SCS monsoon,while the Tibetan Plateau has an important effecton the maintenance of the monso on.The temperature advection in the Indian Peninsul a and the Indochina Peninsula are different because of the land-sea thermal differences in these two regions.