Compared with heavy rainfall on daily scale such as torrential rain, short-duration heavy rainfall (≥20 mm h-1) is a more direct cause of disasters such as mountain torrents, mudslides and urban water logging.Using ground automatic meteorological stations and ERA5 reanalysis data, this study focuses on the temporal and spatial evolution characteristics of short-duration heavy rainfall over the Pearl River Delta region before and after the onset of South China Sea summer monsoon, and explores the possible causes of the characteristics and differences of short-duration heavy rainfall before and after the monsoon onset. Results show that: (1) Compared to those before the monsoon onset, the precipitation over the Pearl River Delta region after the monsoon onset has increased significantly, and the contribution of short-duration heavy rainfall has increased significantly. For the short-duration heavy rainfall itself, the regional average intensity and extremes have little difference before and after the monsoon onset, but the frequency of short-duration heavy rainfall increases by 70.0% after the monsoon onset. (2) The high incidence areas of short-duration heavy rainfall are mainly concentrated in the northeastern part of the Pearl River Delta region and the west coast of the Pearl River Estuary. After the monsoon onset, the frequency of the above-mentioned two areas increased most obviously. The frequency of short-duration heavy rainfall changed from single peak (afternoon) before the monsoon onset to double peak (morning and afternoon) after the monsoon onset. (3) Short-duration heavy rainfall has obvious regional variation characteristics. The average rainfall intensity and extremes of short-duration heavy rainfall after the monsoon onset are significantly stronger in the west coast of the Pearl River Estuary than in inland areas, the frequency peak time in coastal areas changes from the afternoon before the monsoon onset to the morning after the monsoon onset, inland areas are concentrated in the afternoon before and after the monsoon onset. (4) After the monsoon onset, the low-level water vapor during the short-duration heavy rainfall period exceeded 15.6% of the climate mean. Abundant water vapor is transported to the coast under the nocturnal acceleration of the monsoon, and combine with the land breeze to enhance the convergence, which explains the frequency peak time conversion of the short-duration heavy rainfall in the coastal area before and after the monsoon onset. (5) Compared to those before the monsoon onset, the correlation between the frequency of short-duration heavy rainfall and the low-level water vapor flux in the Pearl River Delta region increased significantly after the monsoon onset. The increase of night-morning short-duration heavy rainfall in the coastal areas of the Pearl River Delta region is related to the dynamic forcing caused by the structural change of the wind field in the middle and low layers. The short-duration heavy rainfall before and after the monsoon onset in inland areas is more closely related to the environmental thermal and unstable conditions.These results advance our understanding of the temporal and spatial distribution characteristics of short-duration heavy rainfall before and after the monsoon onset over the Pearl River Delta region and its generation mechanism.