Abstract: City and rural electric network modification, in which hundreds of billion RMB Yuan was invested in our country, was a key project to be carried out across the century. How to make scientific and rational use of the large funds in electric network modification, was a hot issue that government and electric power enterprises paid close attention to. Because the major objective of rural electric network modification was to gain the benefit of saving electric power, this paper centered on analysing wire economic section, 0.4 kV power supply radius and layout mode of transformers distribution.