Abstract: Lake water heat pump(LWHP)is widely used because of its advantages of energy saving and stable operation.But water heat pollution can be generated by the thermal discharge from LWHP.In this paper, the thermal discharge effect of LWHP was analyzed by establishing the lake heat balance model.According to the existing surface water environmental quality standards, and taking the lake water temperature changes as an index, the water heat pollution was quantified by the water heat pollution rate, so a method for evaluating the influence of thermal discharge from LWHP was proposed.By applying this evaluation method to Tianyin Lake LWHP system in Nanjing Institute of Technology, we tested the relevant parameters of the system and the lake water, and obtained the vertical and horizontal temperature gradients of lake water in the hottest and coldest week.The maximum and average water heat pollution rates of the hottest week were 0.69 and 0.48.Besides, the maximum and average water heat pollution rates of the coldest week were 0.42 and 0.38,respectively.Compared with winter, it is more likely to cause water heat pollution in summer.The practice showed that this method can be used to evaluate the influence of thermal discharge from LWHP quantitatively and provides guidance for the design and application of similar LWHP in the future.