Zhuashan Bay watershed is a typical plain river network area to the northwest of the Taihu Lake. In this article, a 1-D hydrodynamic-water quality network model based on MIKE model was established to assess the benefits of water environment treatment projects built in 2012 in the Zhushan Bay watershed. The pollutant reduction effects of the projects were summarized through analyzing the design documents and field investigating the operation techniques and results. Furthermore, indexes of total pollutant amount in the watershed as well as the variations of pollutants into the Taihu Lake before and after the treatment projects were built were calculated. Results revealed that under the constraint of pollutant capacity target, the amount of pollutants to be eliminated reduced from 2011 to 2012, and meanwhile, the amount of pollutants into the Lake also fell down, indicating that the treatment projects had played a positive role in improving regional water environment.