In order to explore the evolution law of the hydrological and meteorological elements in the Xijiang River Basin and to study the potential impact of extreme rainfall on flood runoff, based on the hydrological and meteorological data of the basin from 1956 to 2019, the evolution laws of extreme rainfall, annual runoff, and annual maximum 1-day flood volume were comprehensively analyzed using methods such as trend analysis and mutation test. The Pearson correlation coefficient and double cumulative curve method were used to evaluate the relationship between extreme rainfall and annual runoff. The impact of extreme rainfall on flood disaster losses was discussed. The results show that compared with the upper reaches of the high-altitude area, the changes of extreme rainfall in the middle and lower reaches of the Xijiang River Basin are more obvious, showing increasing frequency and intensity of the extreme rainfall. Rx1day,R99p, and SDⅡ show a significant upward trend, with extreme rainfall indicators mostly experiencing sudden changes in 1992. The average annual runoff and maximum annual flood do not significantly increase, and there exist two mutation points. PRCPTOT, R25, R10, and R95p are significantly correlated with runoff, while R95p, R99p, CDD, R25 have a relatively significant impact on flood disaster indicators. After 2002, the correlation between extreme rainfall indicators and flood disaster indicators has significantly changed.