Global river discharge simulation is conducted taking into account 500 individually operated reservoirs by locating them on the digital global river network map of TRIP, a global river routing model. Operating rule is allocated for each reservoir with a newly developed algorithm that works with currently available global data such as reservoir storage capacity, purposes and simulated river discharge. For irrigation purpose reservoirs, additional operation scheme to interact water demand in lower reach is developed, since irrigation water demand has large seasonal variability and its amount is estimated to reach 85 % of the annual global total water consumption. The model reproduced well the actual reservoir operation and improved river discharge simulation at downstream of reservoirs. Applying the model, the impact of reservoir operation to terrestrial water cycle is examined. The result suggests reservoir operation changes monthly discharge for individual basins substantially (more than 20 precents), although, diminished several percents for continental average. This is partly because the storage and release is canceled out in continental aggregation process, however, mainly; actively controlled reservoir water volume is limited compared with global total runoff.