Abstract: Based on best tracks of the Bay of Bengal storms and the ERA5 reanalysis and persistent extreme precipitation events (PEPEs) in South China during pre-flood seasons from 1979 to 2020, characteristics of the Bay of Bengal storms that have great influence on PEPEs are analyzed. Water vapor transport characteristics of PEPEs influenced by the Bay of Bengal storms and large-scale circulation factors affecting water vapor transport are further investigated using HYSPLIT model and Fuzzy c-means cluster analysis and other methods. Results are as follows. (1) The Bay of Bengal storms during pre-flood season tend to have longer duration and stronger intensity compared to storms in other time periods of the year. There is a significant positive correlation between the duration of storms and concurrent accumulative rainfall in South China. About one third of storms during the pre-flood season have great impacts on PEPEs in South China, and they usually have a larger intensity and a longer life span. (2) The main water vapor transport channels for PEPEs influenced by the Bay of Bengal storms are the south water vapor transport channel and the north water vapor transport channel, while the southerly flows on the west flank of the western Pacific subtropical high also play an important role. Specifically, water vapor convergence along the southern boundary of South China can substantively increase by the south water vapor transport channel. However, the north water transport channel is the main channel for the Bay of Bengal storms, which do not cause PEPEs. (3) From the perspective of large-scale circulation, the anomalous cyclonic circulation and favorable synoptic systems in the upper, middle and lower troposphere result in the occurrence of PEPEs in South China. The key circulation factor is the anomalously strong westerly flow across the equator in South Asian subcontinent on the south of the Indochina Peninsula, which connects water vapor from the Bay of Bengal and South China Sea, ultimately forming the south water vapor transport channel. The above research deepens our understanding of the influence of the Bengal storms on the pre-flood PEPEs in South China. Activities of the Bengal storms and the development and evolution of key circulation factors in the pre-flood season are also a new focus for PEPEs monitoring and forecasting.