By adopting fluid calculation software to establish three dimensional reservoir model and simulating reservoir's natural temperature on design day, the measured temperature was used to correct and treated as the initial condition. According to the annual hourly calculation load of villa cluster, dynamic water temperature and flow were used as boundary conditions. Inputted water surface heat transfer conditions were identified by user defined function based on the data of typical meteorological year. For the distributed drainage combining the discharge network and rainwater pipe network and traditional integrated drainage of reservoir water source heat pump system, dynamic numerical simulation of the water temperature field was conducted. The results show that water's temperature rises 0.33℃ weekly when integrated drainage is adopted and the temperature rises 0.16℃ when distributed drainage is adopted. There is obvious heat accumulation phenomenon when continuous drainage in narrow area works. The simulation of intake water temperature shows that below perennial water level 4.6m depth, the intake water temperature is between 27~23.5℃ from July to October, in which the heat pump system operates efficiently.