High-resolution satellite data are used to analyze the features of the onset process of the tropical Asian summer monsoon(TASM) from the point of the climatology view.It is found that the TASM onsets first over the western region of Indo-China Peninsula,next the whole area of Indo-China Peninsula and the eastern part of Bay of Bengal,and then all Bay of Bengal and South China Sea.However,the enhanced rainfall tendency in Indo-China Peninsula is not more obvious than that in Bay of Bengal and South China Sea after the summer monsoon onset.The 26th to 28th pentad(the first pentad to the fourth pentad of May) is the period of onset process of TASM,during which,the spatio-temporal evolution of low lever wind field corresponds well with convective precipitation,while the sea surface temperature warms one pentad ahead compared to the sea surface wind changing.Mean while,the precipitation of South China is mainly frontal precipitation,named the subtropical monsoon precipitation.The result also demonstrated that using convective precipitation and 10 meters wind field above the sea surface to represent the spatio-temporal evolution of rainfall and prevailing wind of summer monsoon respectively is more accurate and more precise than those routine data.