Based on the ERA5 hourly reanalysis data and the merged hourly precipitation products from National Meteorological Centre from May to June of 2010-2016, low-level jet events over South China are selected and classified using an objective method. The diurnal cycles of boundary layer jet (BLJ) and synoptic-system-related low-level jet (SLLJ) are also investigated during early-summer, as well as their influence on the temporal and spatial distributions of the diurnal cycle of precipitation over South China. The results show that BLJ and SLLJ weaken during daytime while intensify during nighttime, reaching their peaks in the early morning. The diurnal cycles are found to be associated with the clockwise rotation of ageostrophic winds caused by boundary layer inertial oscillations. The precipitation over South China affected by the double low-level jets increases significantly, which shows obvious spatial differences with respect to the diurnal cycle due to the evolution and configuration of double low-level jets. The precipitation in central and northern Guangxi is mainly concentrated over the mountainous area at the left anterior to the SLLJ at nighttime and is characterized by only one single peak in the early morning, whereas in Guangdong and the coastal areas of Guangxi, there are two peaks in the morning and afternoon, respectively. The maintenance of convergence at the BLJ’ exit and mid-level divergence near the SLLJ’s entrance are conducive to the increasing frequency of precipitation and hence emerge the peak in the afternoon. In addition to the favorable configuration of the double low-level jets, the morning peak of precipitation is also attributed to the peak of precipitation intensity caused by the enhanced double low-level jets at nighttime in the diurnal cycle process.