The responses of carbon/water cycles in different grassland ecosystems to extreme climatic events and the underlying mechanisms varied. This study， employed the biogeochemical cycle model Biome-BGCMuSo （BGC with Multilayer Soil Module）， integrated with eddy covariance data，conducted sensitivity analysis and parameter optimization to investigate variations in carbon/water fluxes across different grassland types and their responses to extreme climates. The results showed that carbon flux simulations were sensitive to vegetation photosynthetic physiology and carbon allocation parameters， while water flux simulations were sensitive to leaf and root parameters， with variations across grassland types. Optimizing highly sensitive parameters significantly improved carbon flux simulation accuracy， but water flux simulations still require refinement. During growing season heatwaves， all three grassland types remained carbon sinks， though diurnal carbon sequestration decreased by 28.7% and 29.4% in temperate desert steppe and mountain meadows， respectively. Extreme rainfall enhanced carbon and water fluxes across all three grasslands. Drought events increased carbon sequestration by 62.5% in temperate desert steppe but decreased it by 16.3% in mountain meadows. This study reveals distinct response mechanisms of carbon and water cycles in grasslands of arid-semiarid regions to extreme climatic events， providing scientific basis for predicting the evolution of grassland ecological processes under climate change.

Biome-BGCMuSo model  /  Grassland carbon/Water fluxes  /  Parameters optimization  /  Extreme climate events