Abstract: Land use change is a key factor regulating water conservation function of river basins. Qiantang River Basin is a crucial ecological barrier and water supply source for the Yangtze River Delta region. Understanding the long-term changes in land use and water conservation function has significant importance for regional sustainable development and water security. We used the InVEST model to analyze the changes in land use patterns and water conservation functions in the Qiantang River Basin in 2000, 2010, and 2020, and used random forest model to analyze the driving factors of water conservation function. The results showed that land use conversion in the Qiantang River Basin during 2000-2020 mainly occurred in the transfer among cropland, forest and construction land. A total area of 1317.26 km² of cropland and 158.67 km² of forest had been converted into construction land, while 1301.15 km² of forest had been transformed into cropland. The total water conservation volume of the Qiantang River Basin in 2000, 2010, and 2020 was 1053090.56×10⁴, 1431102.37×10⁴, and 1204484.25×10⁴ m³ respectively, showing a trend of increasing first and then decreasing. There were significant differences in water conservation capacity among land use types. The total water conservation amount during the study period ranked as forest>cropland>construction land>water area>grassland>shrubland>unused land. Precipitation exerted the greatest impact on water conservation capacity, followed by forest area, cropland area and slope. During the study period, the dominant role of precipitation was gradually weakening, while the regulatory effects of underlying surface factors such as forest area and water area had increased. The results would provide a basis for land use pattern optimization and water resources allocation in the Qiantang River Basin, and offer a reference for restoring water conservation functions in other river basins.

Key words: land use change, water source conservation, InVEST model, random forest, Qiantang River Basin