Abstract: The torrential rain forecast during pre-summer flood season in South China attracts a lot of research interests. The rainstorm occurring in prefrontal zone strong shows abrupt and significant regional characteristics, and it's especially difficult to solve in operational forecast, due to its inapparent synoptic scale baroclinity forcing, rich moisture content, strong environmental atmospheric thermodynamic instability, complex triggering mechanism in boundary-layer, external forcing effect of special terrain and land-sea thermal difference. For the torrential rain occurs in prefrontal district, forecasting capabilities of various global numerical weather prediction models used in China Meteorological Administration are very limited, and forecast results of high-resolution meso-scale numerical models are also disappointing. Most of results on torrential rain during pre-summer flood season in South China since the 1970s are reviewed. The unique synoptic and dynamics characteristics are systematically analyzed, such as the first proposing of the rainstorm occurs in prefrontal zone in South China and its typical synoptic scale background, the relationship between the rainstorm in prefrontal zone and the low level jet (LLJ), the formation and propagation of meso-scale convective system (MCS) produced, and triggering mechanisms of the torrential rain. Finally, according to these studies and practical experiences of China Central Meteorological Observatory, synoptic system configurations and triggering factors for torrential rain in prefrontal zone in South China are summarized as three types: The pattern of boundary layer convergence lines, the pattern of southerly wind convergence and the pattern of stronger southwest jet, and scientific problems which require further in-depth study are proposed.