This is a basic study of the performance and characteristics of a cascade heat pump system that uses seawater as the heat source. The operating variables in this study are being analyzed in relation to the seawater heat source temperature, heat exchanger efficiency, and condensation temperature. R410a and R134a are the refrigerants used. Considering the corrosion that may be caused by seawater, a seawater plate heater exchanger with titanium coating was used. In addition, due to large temperature variations of the seawater and hot water, a relatively large and irreversible loss is expected in the compression process. Because of this, a cascade cycle was considered. In this study, the performance was analyzed by EES(Engineering Equation Solver).