As a new kind of ice-storage system, a sub-cooling ice-storage system utilizes the subcooler to improve the evaporating temperature of a refrigerator when simulation result shows that COP of a refrigerator in such a system is about 13% higher than of a conventional static ice-storage system . Because the initial cost of the former is higher than that of the latter , an optimal design is necessary to minimize the overall cost . This paper analyzes some factors affecting the performance of the system. Based on that, some suggestions for the design of such systems are presented,