Climate chande and land use altered the global and regional water cycles. On the ecosystem point of view water cycle can be used to better understanding the interactions among ecosystem, climate change and land use, and hence to better manage the water resources and to make the land use policy optimal. A Dynamic Global Vegetation Model (LPJ) is used to simulate the historical water budget of Chinese ecosystems from 1901-2002 driven by changed climates, increased CO2 concentration and land use change. Preliminary results showed that, the annual runoff and actual evapotranspiration of 102-year averages in the country level gradually increase from the northwest to southeast, reflecting the ecosystem-based feature of water resources in China (higher in forests, medium in grasslands and lower in deserts). Climate change, climate inter-annual variability and enhanced CO2 had the potential to modify vegetation compositions and spatial distributions, thus significantly influenced the long-term water cycles in the country. Runoff increased about 734 billion m³ from the first to second half of the last century, while the actual evapotranspiration remains relatively the same over time. Land use and land cover changes modified the potential water resources of China, positively or negatively depending on regions and time periods. Since 1990 land use reduced the actual evatranspiration and increased the runoff. However great regional differences and temporal fluctuations of runoff occured in the study area. More effectively managing water resoures is an optimal way to mitigate climate change and to reduce water's vulnerability in China.