The distributions of residual flows and dissolved oxygen concentration in the Yellow Sea were simulated and reproduced by an eco-hydrodynamic model which is composed of a three-dimensional hydrodynamic model and an ecosystem model. In order to estimate the environmental capacity of the Yellow Sea, the simulations for predicting the situation of unfavorable environment such as the formation of oxygen-deficient water mass in bottom layer were performed by controlling quantitatively the pollution loads of rivers flowing into the Yellow Sea. The field surveys and the seawater analyses were conducted over the Yellow Sea in summers, 1993 and 1994. The computed residual flows showed the counter-clockwise water circulation to exist in the surface and middle levels and no evident water circulation in the bottom level of the Yellow Sea. In the simulation of water quality with an ecosystem model, the more the pollution loads of 14 major rivers flowing into model region increase, the more evident appear the reductions of dissolved oxygen concentrations around the adjacent areas of estuaries receiving pollutants. In case the pollution loads of all 14 rivers become 7∼10 times as high as the present loads, the concentration of dissolved oxygen appears to be reduced to 5.0㎎ /ℓ or less in the bottom level of the water area being located eastward 60∼120㎞ away from the Changjiang estuary. Therefore, in order to keep the concentration of dissolved oxygen being 5.0㎎O₂/ℓ and above, which is the Korean criterion of the third class seawater quality, the environmental capacity of the Yellow Sea may be estimated to be 7∼10 times as high as the present pollution loads.