In order to maintain the water balance and water quality stability of the landscape water body in the closed artificial lake, the technical means of sponge city construction is adopted to explore the ecological design so that it could guide the ecological restoration of the urban closed water body. The water balance, hydrodynamic simulation, and ecological water construction of a closed artificial lake on Changxing Island according to the local meteorological data of Chongming and the current situation of the project design were analyzed in this study. The results showed that the artificial lake catchment area was supplemented by external water for eight months of the year. The maximum water demand was 80.6 m3 per day. There were 667 m2 subsurface flow constructed wetlands designed to treat external supplement water. The flow velocity was 0~0.02 m/s, and the overall flow velocity was very slow. Emergent plants such as Iris wilsonii, Pontederia cordata, and Juncus effuses could be mainly planted in the slow flow area to create an ecological revetment and dotted planted with a plant height of more than 1 m, such as Lythrum salicaria, Typha angustifolia, and Canna glauca. Floating leaves and submerged plants were mainly Nymphaea tetragona, Vallisneria spiralis, Ceratophyllum demersum, and Hydrilla verticillata. Therefore, the water resources stability and water quality health of the closed artificial lake can be maintained through the scheme design of hydrodynamic optimization, artificial wetland treatment, and aquatic vegetation construction.