Aiming at the wind-driven current in Lake Taihu, a calculation method of combining joint frequency of wind directions, wind speeds and pollution zone control was used to study the capacity of water environment for Lake Taihu. A 2-D unstable-state model of water quantity and quality in Lake Taihu was established. By using hydrological data, the fields of flow and concentrations were numerically simulated, and the simulations were inter-compared. The pollution zone control method which is used to calculate the water environmental capacity was advanced by considering the affect of the speed and direction of wind. Control principia are single pollution control areas between 1 km² and 3 km², and the total length of pollution zone less than 10% of land line. The CODCr capacity of Lake Taihu is 132727 t/a, and TN is 7700 t/a.