The changes of inflow and outflow runoff and sediment of the Three Gorges Reservoir before and after the impoundment are systematically analyzed based on the observed data of hydrographic stations. The results reveal that since the 1990s, the inflow-outflow runoff and sediment have both reduced, of which the sediment discharge reduced much more remarkably than the runoff. In recent years, the inflow  outflow runoff and sediment during flood season remain above 76% and 96% of the whole year. In terms of annual distribution, the inflow runoff and sediment in flood season both exhibit a tendency of decreasing; whereas the outflow runoff tends to decrease and the outflow sediment tends to increase in flood season. After the impoundment, the inflow and outflow water and sediment decreased sharply in September and October, while increased in dry season from February to April.