As the water body of Youhu gulf in Suzhou has increasingly become serious，so it is necessary to carried out ecological restoration project such as water system reconstruction, sediment ecological dredging ,macrophyte restoration and biomanipulation and so on. Aimed at improving water environment,the paper investigated the water situation of restored and un-restored area from April 2010 to February 2011. The results showed that water exchange and macrophyte have been improved, and the integrated water quality of the ecological engineering area inhance from Ⅳ to Ⅲ of national class. Water quality in ecological restoration area is significantly better than that of outside during the same period. The concentration of DO and transparency in restoration area increased by 29.92% and 25.22% respectively compared with the un-restored.The concentration of CODMn, TOC, TP, TN, NO3--N and NH4+-N respectively decreased by 17.31%, 12.13%, 46.07%, 65.93%, 77.72% and 60.19%.The abundance of phytoplankton got control and the ecological restoration area was improved. The water quality of outlet is obviously better than that of inlet.