Abstract: The decadal variation of precipitation in March over South China and its relationship with PDO(Pacific Decadal Oscillation) are analyzed by using the observational rainfall data, PDO index, and NCEP reanalysis data. The Mann-Kendall test performed on precipitation in March over South China shows that the turning year for decadal change in about 1978, precipitation experienced a notable low to high transition. In the decadal period of low rainfall, PDO is in negative phase (high sea surface temperature in the North Pacific, low sea surface temperature in the middleEast Pacific), sea level pressure and height at 500 hPa in North Pacific are high, sea level pressure and height at 500 hPa on the Asian continent are low, the troposphere atmosphere in East Asia is warm, the western Pacific subtropical high is easterly, East Asian uppertropospheric jet stream is northerly, Hadley circulation in East Asian is weak. In the decadal period of high rainfall, PDO is in positive phase, the situation is completely the opposite. The variability of the precipitation in March has a very significant correlation with PDO index in February and March, the correlation coefficients between them were positive at 99% confidence level. It can be summed up the changes of precipitation in March over South China is closely related to the changes of sea surface temperature in the North Pacific Ocean on decadal time scales, and a possible mechanism is proposed about how the PDO influences the precipitation anomaly over South China in March.