Taking the water temperature of lakes and reservoirs as the research object, a lake water temperature calculation model was built.The correctness of the calculation model was validated by comparing the model results with measured data. The variation and influencing factors of the water temperature of lakes and reservoirs in Changsha area were studied with the model.The load capacity of heat and cool supply of lakes and reservoirs were calculated, and the influencing factors of the load capacity of the heat and cool supply were analyzed.The results can provide references for the design of water source heat pump system using lakes and reservoirs as the heat source.