Abstract: Using conventional observation data, radar data, FNL (1°×1°) and ERA5 (0.25°×0.25°) reanalysis data, the warm-sector rainstorm process in Ya 'an from 15 to 16 September 2024 was analyzed. The results show that the circulation pattern at 500 hPa was high in the east and low in the west. Easterly wind, diverted from the outer flow on the west side of the typhoon, entered the basin along the south side of subtropical high and turned to southerly wind, which intensified overnight, providing sufficient moisture to the heavy rainfall area. Under a conditionally unstable stratification characterized by high energy and humidity, the low lifting condensation level and level of free convection allowed convection to be triggered by weak dynamic lifting. A thick warm cloud layer contributed to high precipitation efficiency. The initial convection was ignited by low-level wind field disturbances combined with topographic lifting. The subsequent organization and development of convective cells ultimately led to the heavy rainfall event.