Two dimensional hydrodynamic model was used to simulate the hydraulic and thermal characteristics of thermal discharge during spring and neap tides under the combination schemes of three intakes and three outlets of Third Stage project in a power plant in semi-enclosed waters, and to analyze the influence of different schemes on the temperature rise distribution and excess temperature at intake. The results show that: For the semi-enclosed waters, neap tide is unfavorable tidal type, because the heat accumulation is more obvious and the areas of maximum and average temperature rise are larger than that in spring tide. When outlet is closer to bay mouth, the heat transfer is better and the area of temperature rise is greatly reduced. For the drainage schemeⅠwhich is closer to the bay mouth, the average temperature rise area of 1 ℃ is about 36% of the area of scheme Ⅲ. Under the same intake scheme of the Third Stage, the average excess temperature at intake is about 0.3 ℃ lower than that of other drainage schemes. The drainage schemeⅠhas obvious advantages. However, the maximum intake temperature rise of the First and Second Stages is higher because the drainage scheme I is close to the intake, so the diversion dike is considered to optimize the scheme. The diversion dike could reduce the maximum intake temperature rise of the First and Second Stages by about 0.6～0.7 ℃ and the mean by 0.1～0.2 ℃, suggesting that the diversion dike is an effective tool to reduce the heat return. The results are valuable for the layout and optimization of intake and outlet, and the study of thermal characteristics for similar waters.