Assessing the future water balance of regional terrestrial ecosystems is one of the important scientific problems in ecosystem and global change research. Using historical and future climate scenarios generated from IPCC-related climate models as input to the terrestrial ecosystem model and considering changes in CO_2 concentrations,we study the effects of climate change and CO_2 concentration doubling on China's future water resources. The results show that the average precipitation in China is gradually increasing, the temperature level is increasing, and the evapotranspiration levels show the trend of sustained growth, and the runoff is the emergence of different wet and dry season. In the scenario of doubled CO_2 concentration,the evapotranspiration is slightly lower than that under non-doubled CO_2 concentration, while the runoff is slightly higher than that in non-doubled CO_2 concentration scenarios. The performance will be more obvious after 2050.