A large number of seawater-source heat pump systems (SWHP) have been used in residential and commercial buildings in coastal areas due to the attractive advantages of high efficiency and environmental friendliness. To overcome the disadvantages of the open loop SWHP in winter of cold regions, a closed loop SWHP system with casted heat exchanger (CHE) is presented in this paper. The CHE is consisted of pipes immersed in the seawater and used for transferring heat between the seawater and the heat exchanger pipes of the SWHP. In addition, two mathematical models that described heat transfer process of CHE in the icing and non-icing conditions in winter have been developed and validated by an experimental study. The temperature distributions along the CHE were compared between the experimental data and numerical simulation results. The relative error is less than 5%. As a result, application of SWHP systems with CHE in coastal areas in China is feasible due to the favorable geographical conditions and environment.