Abstract: On August 7-8, 2025, Yuzhong County, Gansu, experienced a historic extreme precipitation event. The Xinglongshan station recorded 220.2 mm of rainfall over 15 hours, accounting for 56% of the annual average precipitation. This extreme rainfall, characterized by exceptionally heavy downpour magnitudes, triggered severe flash floods that affected multiple townships, resulting in 15 fatalities and 28 missing persons. To conduct an in-depth analysis of the extremeness characteristics of this event, this paper utilizes multi-source data and employs diagnostic analysis, precipitation extremeness indices, and thermal parameters to examine the weather conditions, circulation patterns, extremeness features, and evolution of key thermal parameters during this extreme rainstorm. The results are as follows. (1) This event was characterized by a long duration, high cumulative rainfall, high short-duration rainfall intensity, and pronounced local nature. A total of 15 short-duration heavy rainfall events were recorded at stations across Yuzhong County, with the Xinglongshan station experiencing continuous short-duration heavy rainfall for 6 hours. Among the 16 stations in the province recording rainfall exceeding 100 mm (torrential rain), four were located in Yuzhong. (2) The synoptic pattern featuring a "two-trough-one-ridge" configuration at 500 hPa, combined with the periphery of the Western Pacific Subtropical High (hereafter referred to as the Subtropical High), jointly maintained a high-energy, high-humidity environment. The shear line at 700 hPa served as the primary dynamic lifting trigger mechanism. Coupled with abundant moisture transport and orographic lifting over Maxian Mountain, these factors created favorable conditions for the development of this heavy precipitation event. (3) Precipitation extremeness indices further reveal that the 78-station event-total precipitation, 37-station hourly rainfall intensity, and 79-station frequency of short-duration heavy rainfall in central Gansu all broke the historical August extremes since station establishment, exhibiting significant spatial heterogeneity. Yuzhong County and eastern Linxia Hui Autonomous Prefecture were the strong centers of this event, with daily precipitation at stations such as Xinglongshan exceeding 100 mm, reaching twice the historical extreme value. (4) Quantitative analysis of key thermal parameters and precipitable water unveiled the triggering and maintenance mechanisms of the event. Prior to the event, multiple severe convection parameters exceeded the 95% extreme threshold of the past decade, indicating the presence of extreme instability energy in the atmosphere. Simultaneously, precipitable water persistently surpassed the 95th percentile of the past decade at multiple time steps. The southwest low-level jet along the Subtropical High periphery, combined with orographic lifting, formed a stable "moisture-energy" transport belt. This spatiotemporal coupling of "high potential instability" and "anomalously abundant moisture", enhanced by the terrain-induced blocking and convergence on the shear line, constituted the core physical mechanism responsible for precipitation breaking historical records. (5) The study, utilizing satellite data, provides key forecasting criteria for localized sudden extreme precipitation events under the Subtropical High periphery circulation pattern. These criteria include topographic convergence coupled with satellite-retrieved thermal parameters exceeding extreme values, offering a more refined quantitative basis for forecasting localized sudden extreme precipitation in complex terrain areas of Northwest China.