Abstract: This study investigates the physical link between the convection associated with the BOB monsoon vortex and the SCS summer monsoon onset, as well as the mechanism of the evolution of the low-level subtropical anticyclone over the SCS through numerical experiments. It is shown that introduction of heating over the BOB results in vigorous convection over the BOB, and the BOB monsoon onset,as well as the development of westerlies and vertical ascent over the northern SCS region due to an asymmetric Rossby-wave response. Together with the low-level moisture advection, convection is induced over the northern SCS. It is the condensation heating over the northern SCS that causes the overturning of the meridional gradient of temperature over the SCS. Consequently the subtropical anticyclone in the lower troposphere over the SCS weakened gradually. Eventually as convection develops over the entire SCS domain, the subtropical anticyclone moves out of the region.