Based on the surface-water heat pump system, this paper established a heat transfer model for casted heat exchanger. An experimental study was carried out to test the validity of the model. The casted heat exchanger was consisted of pipes immersed in the surface-water and used for transferring heat between the water and the heat exchanger pipes of the surface-water source heat pump. A programme was developed in VB environment and the effects of inlet temperature and flow rate of the secondary refrigerant, length of the casted heat exchanger and the temperature of the surface-water on the results were investigated. The results of the numerical simulation were in consistence with the experiments on both winter and summer conditions.