The coastal area of south China, one of the biggest population and economic centers in the world, is a region of abundant rainfall throughout the warm season. Under the influence of warm, moist monsoon flow, there are strong and complex diurnal variations of precipitation in the region. Based on long-term radar observations and convection-permitting numerical experiments, we found that the diurnal variation and propagation of the coastal precipitation over the region is mostly controlled by the interactions between the land-sea breeze circulation and monsoonal onshore wind. While, coastal terrains, inland surface friction, cold pool dynamics and environmental moisture content also show considerable impacts on the diurnal variation of coastal precipitation by modifying the initial timing, propagating speed and intensity of the coastal rainfall.