Abstract: Water resources management and regulation in the Ganjiang River Basin face significant challenges in the context of climate change. The projection and trend analysis of future precipitation and runoff in river basins have become a current research necessity. This study employed the MK trend test and linear propensity estimation to forecast spatiotemporal changes in precipitation in the Ganjiang River Basin under SSP2-4.5 and SSP5-8.5 scenarios from 2015 to 2100, using data from six climate models of the CMIP6. Future annual runoff simulation and trend analysis for the basin were conducted using the VIC hydrological model, with the occurrence of runoff mutations determined through a combination of the MK mutation test and the sliding T-test method. The results indicated that future multi-year average precipitation and runoff in the Ganjiang River Basin under six climate models are projected to increase to varying degrees compared to the baseline period. The overall trend for future annual precipitation and runoff is expected to rise. Future projections indicate an increase in precipitation and runoff during the flood season in the Ganjiang River Basin, while a decrease is anticipated during the dry season. The magnitude of these changes is more pronounced under the SSP5-8.5 scenario compared to SSP2-4.5, exacerbating the uneven distribution of water resources throughout the year. The annual runoff mutation test revealed extreme runoff in eight mutation years, including 2076. This study provides support and reference for the future planning of water resources and flood/drought warning systems in complex mountainous basins.