Abstract: The data of atmosphere and ocean elements, including turbulent momentum, radiation, SST, wave, carbon flux, and air temperature, humidity, wind at heights of 3.5 m, 7.0 m, and 10.5 m, were observed in the fourth air sea flux experiment during the monsoon at the Xisha islands in South China Sea (SCS) from April to October in the year 2008. The air sea flux variation and heat balance were studied during the onset, development, break and decay of the SCS monsoon, as well as the processes of rainstorms, typhoons and cold currents, using the computational results in light of the scheme of eddy correlation and COARE3.0 parameterization. The results are as follows: in the clear days before the onset of the monsoon, total radiation was high and the loss of heat of the sea was low, so the net heat gain of the sea was quite high and the SST increased rapidly. During the onset, the total radiation was still high, and the long wave radiation of the atmosphere was strengthened while the long wave radiation of the sea stabilized, so that the net heat gain of the sea was still positive. The sensible heat (H S) flux was high when the monsoon was active, especially in raining days, and the HS flux decreased at the break of the monsoon. Though the latent heat (HL) flux was high when the monsoon is active, the net heat gain of the sea was still positive because the solar short wave radiation was of high value. At the break of the monsoon, the HS and HL fluxes were reduced, and the seas gain more heat than when the monsoon was active. When it was raining, the solar short wave radiation decreased and the HS flux augmented with the result that the sea lost much heat and the SST decreased fleetly. During the decay of the SCS monsoon, the humidity and the HL flux decreased, so the net heat gain of the sea was positive, and the SST rose. Under the influence of the typhoons, the HL flux increased rapidly with the augmentation of wind speed. The HS flux was low in clear days and increased acutely in rainy days. Because the solar short wave radiation decreased and the HL increased rapidly, the net heat gain of the sea was negative, so the SST was reduced. The momentum flux was mainly related to the wind speed at the sea level. These two elements are related using:τ= 0.00171v2-0.003809v+0.02213.