The pre-flood season (also named as early rainy season) in South China in 2012 begins in the 2nd pentad in April, and ends in the 5th pentad in June. The pre-flood season has experienced three different periods. The first one is the frontal precipitation period from 2nd pentad in April to 3rd pentad in May, with precipitation over 25% more than normal in most Jiangnan area and most South China. The second period is the dry period from 4th pentad in May to 2nd pentad in June, with precipitation over 50% less than normal in central and eastern South China. The last one is the summer monsoon precipitation period during 3rd-5th pentads in June, with precipitation over 50% more than normal in southeastern Jiangnan area and central-western South China. Analysis of the atmospheric circulation anomalies during each period of the pre-flood season in South China in 2012 indicates that after the pre-flood season onset, more frontal precipitation during the first period is caused by the increased high ridge over the Ural Mountains and the anomalous convergent moisture flux in South China due to the intensified low-level western Pacific subtropical high (WPSH); during the dry period, the South China Sea summer monsoon (SCSSM) is weaker and the WPSH abnormally shifts northward for three pentads. In the last summer monsoon precipitation period, the anomalously intensified SCSSM, the southward WPSH, as well as the enhanced monsoon trough over the Bay of Bengal favor anomalously more precipitation in South China.