A mathematical model of three-dimensional wind-driven current is developed with the consideration of local wind system in Taihu lake. The simulated results on the current circulation are more consistent with the observed data, especially on current speed, in comparison with the simulation with respect to two-dimensional models. In addition, it shows that the topography of the lake basin influences on lake circulation, and the existance of the Xishan Island strongly enhances the current speed in the area between Xishan and Dongshan Islands. The convergence field in Taihu lake induced by different wind directions which influence directly on the distribution of the alga in Taihu lake is computed and analysed. Considering the two bays in the north area of Taihu lake, the convergence field can be divided into three patterns: (1) convergence patterns under S and SW winds: (2) divergence patterns under N and NE winds; and (3) convergence and divergence patterns under W, NW, E and SE winds.In terms of the simulated results. the concentration of blue-green alga in Taihu lake can be known roughly.In conclusion, three-dimensional model is better than two-dimensinal model in simulating wind driven current in large shallow lakes such as Taihu lake. The long corridor between Xishan and Dongshan Islands in Taihu lake is very important to the formation of the lake circulation. The three patterns of convergence fields which result in the different distributions of the concentration of the alga are classified in the paper according to the different wind directions.