The water gate is an important component of the structure of ancient city walls, and it is very critical to research on the layout and evolution of ancient city walls. In order to create a scientific plan for conservation of the water gate relics at Taizhou, an on-site survey was first done to analyze the state of deterioration. Visible problems were discovered, including damage to the wall, foundation, arch and timber piles. Then the structural performance was assessed by finite element modeling (FEM) analysis. Potential problems with the foundation and wall were found. Finally, a plan of repair was proposed for the water gate, including strengthening of the foundation and wall and preservation of the timber piles, based on the results of damage investigation and theoretical analysis.