To lower cost and improve power supply quality, the economic power supply radius of a substation is investigated. First, taking the construction cost as well as operation and maintenance cost into consideration, an economic power supply optimization model of the substation to minimize the annual supply cost of per unit area is established and a solution method is provided. Then, the quantitative relationship between power supply radius and voltage loss of lines under different load scenarios is also established, through which the voltage quality of optimized economical power supply radius is examined according to voltage loss regulation in the distribution network. The correctness and effectiveness of the proposed method are verified using actual distribution network data. The result provided can be used as a reference in regional distribution network planning. This work is supported by the Key Science and Technology Project of China Southern Power Grid Co., Ltd. (No. 059100KK52190009).