In July 2021, a rare and extremely severe rainstorm and flood disaster occurred in Henan Province, China. Using multiple daily observational and reanalysis data, this study investigates the modulation mechanisms of the boreal summer intraseasonal oscillation (BSISO) on the Henan extreme rainfall event. The analysis is conducted within the framework of the dual-mode BSISO indices (BSISO1: 30–60-day oscillation; BSISO2: 10–30-day oscillation), employing wavelet analysis, dry and wet phase analysis