Abstract:The warm-sector rainstorms over the Sichuan Basin were defined and classified into four types based on the synoptic situation, including the southwest vortex (SWV), the edge of subtropical high (ESH), the southwest jet (SWJ), and the southeast wind (SEW) types. By using the conventional and the hourly precipitation data of automatic weather station from May to September during 2008-2018, we statistically analyzed the spatio-temporal distribution of warm-sector rainstorms and the nature of precipitation as well as the mesoscale characteristics and causes for their formation. The major characteristics obtained from the research are that the four types of warm-secfor rainstorms usually occur in windward slope of mountain, bellmouth topography and near the uneven surface which is transitional zones between plain, hills and uplands, etc. The SWV and SWJ types have a large area, and the former mainly occurs in the middle and south of the basin and the latter from the middle of the basin to the north of Longmen Mountains and Daba Mountains. The ESH and SEW types are decentralized precipitation, and the precipitations usually occur in the west of the basin. All the four types of precipitation have substantial diurnal variation, showing a single peak type, which is strengthened at night but weakened during the day. The warm-sector rainstorms consist of stable and convective precipitations. The heavier the daily rainfall is, the more obvious convective nature the precipitation has, of which, the convective precipitation of ESH and SEW types is obvious, 〖JP2〗and the stable precipitation of SWV and SWJ types is obvious. The warm-sector rainstorms are directly caused by the development of MβCSs, the lifetimes of SWV and SWJ types are ≥6 h,〖JP〗 and those of ESH and SEW types are ≤6 h. All the four types of convective precipitation (20-50 mm·h-1) last for no more than 3 h, and the flash heavy rain (≥50 mm·h-1) lasts for no more than 1 h, otherwise, it is very easy to cause extreme precipitation events. SWV and SWJ types are prone to extreme heavy rainfall. The four types of rainstorms occur in the unstable environment with high energy and high humidity. The average CAPE value is more than 1 〖KG-*5〗000 J·kg-1, K index is about 40 ℃, θse of 850 hPa is about 85 ℃, and the average specific humidity can reach 16 g·kg-1。