Based on the daily outgoing long-wave radiation (OLR) dataset from NCEP/NCAR during 1979－2004, the features of the zonal and meridional propagations of the tropical convection during the onset period of the South China Sea (SCS) summer monsoon (SCSSM) are analyzed in this paper. Results indicate that the directions of both the zonal propagation and the meridional counterpart are quite different. For example, for the zonal propagation, the deep convection can propagate either from the Bay of Bengal (BOB) to SCS, or from the western Pacific to SCS, or developed locally. But during the onset period of the Indian summer monsoon, the zonal propagation is relatively simplex with a westward propagation. For the meridional direction, the convection over SCS can be influenced by both the counterpart from the tropical regions of the Southern Hemisphere and from the middle latitudes of the Northern Hemisphere. But in the Indian monsoon regions, the convection comes only from the Southern Hemisphere. These observation results reveal that the convective activities during the onset period of SCSSM are more complex than those of the Indian summer monsoon. Results also show that the different retreat ways of the western Pacific subtropical high in the lower troposphere can lead to the multi-direction propagation of the deep convection over SCS. This will misrepresent the judgment of the onset dates of SCSSM.