Abstract: With the large-scale access of new energy such as wind power, photovoltaic and biomass, the management of power grid loss reduction is facing a great challenge.In this paper, the statistical line loss rate calculation model of 220 kV main transformer is established, The analysis shows that "with the continuous increase of local power sources such as new energy, the line loss rate will change from decreasing to increasing.In order to deeply analyze the impact of power output on line loss and obtain the extreme value of the line loss rate, an analysis method based on actual operation data is proposed.The source load ratio coefficient is introduced and the historical data is used for quadratic function simulation to obtain the theoretical source load ratio corresponding to the minimum value of the line loss rate.