AbstractTerrestrial ecosystem water retention (TEWR) service is subject to climate change and elevated atmospheric carbon dioxide concentration (eCO2), however, the relevant processes by which future climate change and eCO2 affect TEWR are poorly understood. Here, we use the factorial simulation experiments from the Inter‐Sectoral Impact Model Intercomparison Project to address this research question. The experiments are based on three dynamic global vegetation models forced with the same climate change scenarios. Results suggest that compared to the preindustrial level, during 2070–2099, (a) TEWR change is highly uncertain, especially in the Southern Hemisphere. (b) Climate change will dominate the pattern of future TEWR change compared with eCO2. (c) Precipitation and runoff change will dominate the future TEWR change in various regions, and the direct role of evapotranspiration (ET) on TEWR will be relatively small. (d) eCO2 will mainly affect vegetation dynamics in energy‐limited regions to affect the runoff, and consequently affecting TEWR change. (e) eCO2 will decrease ET and increase the runoff, resulting in a slight TWER change. These findings improve the understanding of the responses of TEWR to future climate change and eCO2.