Abstract: This paper is devoted to the features of sea-surface heat exchange in the different phases before and after the summer monsoon onset in the South-China Sea (SCS) by analysis of the observed air-sea heat fluxes of year 2000 and 2002 and dat a from Xisha Island Weather Station in the same period. Results suggest that the primary factors af fecting sea-surface thermal budget are the latent heat flux and the net short wave radiation because the sensible heat fluxs and net long wave radiation have low magnitude or a smaller change range, but the net solar short wave radiation and the latent heat flux have high value and bigger change range which the daily mean value could differ almost fivefold. The comparison analysis finds that there is better relation between the low cloud amount and the net short wave radiation. The sharp reduction of the net short wave radiation is usually in association with precipitation. Among the different phases before and after the summer monsoon onset in the South-China Sea (SCS), the variations of the net solar shortw ave radiation and the latent heat flux have different ways. In the phase before the summer monsoon onset or break phase, the variation range of the latent heat flux is smaller but the net short wave radiation maintains high value. In the onset or active phase, there is complex change among them. In year 2000, during the first emergence of southwest monsoon, the net loss happened due to the dramatic diminution of the net shortwave radiation resulting from increased cloud system and intense precipitation, which was a situation of local convection that the ocean release energy to atmosphere in the form of precipitation; In the second span of the gales, there was lit tle change in the net solar short wave radiation because of less precipitation cloud system, but the dramatic growth of latent heat flux resulting from int ense evaporation could be responsible for vapor transport faraway from the source by means of large-scale strong SW winds. Regardless of t heir changing ways, the thermal gain was reduced or became net loss at the active stage or the onset stage and the thermal gain gradually increased before the onset stage or in the lull periods; That means the monsoon burst or active process is the process that ocean release the energy and the monsoon break process or the period before the onset is the process that ocean gain the energy. It is also found that the variation of SST is not synchronous with that of sea-surface thermal budget. Owing to great thermal inertia of water, SST change lags behind that of heat budget over the sea surface, and the lagging is responsible for regulating the budget by affecting latent heat f luxes, which, in turn, effected upon the change of the SST, thereby forming short-term oscillations that are in association with the active/break phases of the monsoons. Part of the conclusions have been borne out by the observational study based on 1998.