To understand the impact of the second phase of the South Channel Regulation Project on the nearby Jiuduansha Reserve,various research methods such as physical models,mathematical models,and biodiversity impact assessment models are adopted to study the impact of the proposed second phase of the South Channel Regulation Project on the tidal flats,wetlands,and biodiversity of the Jiuduansha Reserve.The results show that the implementation of the second phase of the South Channel Regulation Project is conducive to alleviating the erosion trend along the southern edge of the middle part of the tidal flats in the Jiuduansha Reserve and can increase the wetland resources in the reserve by approximately 1.33 km2.The construction of the expansion embankment and channel dredging in the second phase of the South Channel Regulation Project have no direct adverse impact on the aquatic biological resources in the Jiuduansha Reserve,and the degree of impact on the biodiversity of the Jiuduansha Reserve is of medium to low intensity.To address the loss of benthic organisms caused by the second phase of the South Channel Regulation Project,it is necessary to carry out restocking activities during the project implementation and subsequent maintenance to replenish and enrich the biological resources in the project area.The second phase of the South Channel Regulation Project has a relatively small overall impact on the tidal flats and wetlands of Jiuduansha Reserve,and the project is feasible.