Abstract: An extreme rainfall event occurred in Qinghai on August 13, 2022, causing severe disasters including floods and landslides, the extreme rainfall also indirectly triggered the deadly flash flood in Datong County on August 18. Based on high-resolution multi-source observational data and ERA5 reanalysis data, this study analyzed the rainfall characteristics, synoptic systems, and environmental conditions of this event, incorporating topographic effects, using the HYSPLIT4 trajectory model, percentile methodand and standardized anomaly calculation. The results show that the extreme rainfall occurred in the eastern valley regions of Qinghai and the windward slope of Laji Mountain, characterized by high cumulative rainfall, intense hourly rainfall, long duration, significant extremeness, and severe disaster-causing impacts; the anomalous westward and northward positioning of the Western Pacific subtropical high and the unusually strong South Asian high were the synoptic-scale circulation backgrounds conducive to the occurrence of extreme rainfall; θ_se was anomalously strong over 3-4σ, with a deep convective instability structure and strong convective available potential energy, providing thermal and instability conditions for the development of mesoscale convective systems and extreme rainfall; the low-level meso-γ-scale shear line, wind convergence, and frontal zone led to an anomalously strong convergence on 700 hPa in the rainfall region, with a value of 3-4σ above normal, abundant moisture formed a moisture convergence center with a value above 5σ in the rainfall region, the strong convergence on the low level generated intense vertical upward motion, triggering the release of convective instability energy, lifting and condensation of moisture, which induced extreme rainfall; the eastward airflow was forced to ascend after encountering the topographic barrier of Laji Mountain, resulting in the continuous generation, development, merging, and slow movement of mesoscale convective cloud clusters, which contributed to the long duration and high cumulative rainfall of the extreme rainfall.