The design temperature difference between chilled water supply and return of district cooling systems is usually considered by using empirical values or only from the view point of energy consumption. In this paper, an optimization model of temperature difference between the chilled water supply and return of a district cooling system (DCS) was established with dynamic annual commuted cost method from the economic aspect. This model was used to optimize the temperature difference of the chilled water of a district cooling system in a community in a zone hot in summer and cold in winter. Besides, the influence of power price, specific frictional resistance, cooling supply distance and air conditioning load on the economic temperature difference was also analyzed. The results have shown that annual cost is the lowest when economic temperature difference is 6.3℃ and the corresponding design chilled water supply temperature is 5.9℃. Compared with the conventional design temperature of 7/12℃, it saves RMB 24,000 a year and the economic benefit is remarkable. Moreover, the economic temperature difference decreases with the growth of power price and increases with the growth of specific frictional resistance, cooling supply distance and air conditioning load.