To research the accumulated impact of thermal discharge from established and proposed power plants in Tieshan Bay, Delft three dimensional (Delft3D) hydrodynamic model was adopted to simulate the tidal current and temperature field. Based on sensitivity analysis of key spatial and temporal parameters, the computation time is twenty five tidal periods, the minimal mesh size is 40 meters, and the time step is 15 seconds. The numerical results showed: local current fields in the vicinity of new projects were changed due to the shoreline variation when proposed power plant is in operation; the 1 centigrade (1℃) isothermalincrement line overlapped with Beihai Power Plant; the impact area was increased by 21 square kilometers; the intake water temperature of Beihai Power Plant rose 0.4℃. Comparison between numerical model and physical model revealed that the simulation results have bigger differences in the near field, but as the thermal discharges move far away from water outlet the differences become smaller and the two models have almost the same impact area near 1℃ isothermalincrement line.