Line loss rate is an important economic index to reflect the operation level

loss reduction technology and management level of power grid. With the development of economy

the structure of load utilization will change

which will affect the line loss rate of power grid. Considering the input and output in the process of power transmission and the line loss in the process of electricity sales

this paper develops a line loss rate model at each voltage level. Then the influence of electricity sale proportion on the line loss rate at each voltage level is quantitatively analyzed based on this model. Then the electricity sale proportion is calculated when the line loss rate at each voltage level is minimum. The example shows that the variation of line loss rate at each voltage level can be obtained by the proposed model when the electricity sale proportion changes

which is helpful to control the future variation of line loss rate and enhance the economical efficiency of power grid.