This paper presents a study on the temporal and spatial variations of the precipitation over the　area of the South China Sea (SCS) during the monsoon onset period.The data used are from the Tropical　Rainfall Measuring Mission (TRMM) observations between April and June over the nine years from 1998 to　2006.This study focuses on the central and northern part of South China Sea (110-120°E,10-20°N).Based on the observations,the 27th pentad is selected as the occurrence time of the SCS monsoon onset.The conclusions are as follows.(1) After the monsoon onset,the specific area,defined as the ratio of the number of pixels with certain type of precipitation to the number of total pixels,extends significantly for both convective and stratiform rain,with the latter having a larger magnitude.The specific rainfall,defined as the ratio of the amount of certain type of precipitation to the total amount of precipitation,decreases for convective rain and increases for stratiform rain.(2) Results also show significant increase in heavy rain and decrease in light rain after the monsoon onset.(3) Changes are also observed in the rainfall horizontal distributions over the SCS before and after the monsoon onset,manifested by the relocation of precipitation minima for both convective and stratiform rain.(4) After the monsoon onset,the variability in characteristics of precipitation vertical structure increases significantly,leading to more latent heat release and consequently deeper convection.Meanwhile,the bright-band altitude of stratiform precipitation is also elevated.