Abstract: Affected by Typhoon Maysak (the 10th typhoon of 2026), a historically rare and exceptionally severe rainstorm event occurred in Guangxi from 08:00 BT 3 to 08:00 BT 9 July 2026, causing severe disasters. This study investigated the precipitation characteristics and underlying causes of this extreme rainstorm event using multiple data sources, including conventional surface and upper-air observations, national and regional weather station precipitation records, typhoon track and intensity, radar measurements, and ERA5 reanalysis data. The results show that the event was characterized by large accumulated rainfall, highly concentrated heavy rainfall, and prominent extremeness. Torrential rainfall occurred in Qinzhou, Fangchenggang, Nanning, Guigang, and other cities, with accumulated precipitation exceeding 600 mm and locally exceeding 1 000 mm. The extreme precipitation is mainly distributed from the coastal areas to southern Guangxi. Based on the dominant synoptic-scale weather systems, radar echoes, and heavy precipitation characteristics, the precipitation process can be divided into three main stages. In the first stage, the heavy rainfall was concentrated and locally intense. In the second stage, the heavy rainfall area was the largest and the intensity was the highest. In the third stage, extremely heavy rainfall areas were scattered and more closely related to terrain. This extreme torrential-rain event occurred under a large-scale circulation background characterized by a two-trough-one-ridge pattern in mid-to-high latitudes, a stable continental high and the Western Pacific Subtropical High, a saddle-shaped pressure field over western South China, the slow passage of Typhoon Maysak across Guangxi, and the northward advance of vigorous monsoon flow. The strong monsoon flow was entrained into the typhoon circulation and supplied persistent and abundant water vapor and energy. Intense deep low-level convergence and upper-level divergence provided steady and powerful dynamic forcing. The maintenance of a low-level warm-moist environment and convectively unstable stratification, combined with vigorous upward motion, was an important contributor to the generation of extreme heavy rainfall.