In order to discuss the energy efficiency of overhead lines under the influence of voltage fluctuations and flicker,the short line model is used to qualitatively analyze the various losses of overhead lines in voltage fluctuation and flicker. Within the scope of the national standard, the fluctuation amplitude and the fluctuating frequency step are set, and the simulation is carried out.The simulation results show that the additional loss of the overhead line is positively correlated with the primary of the frequency fluctuation, and negatively correlated with the primary and cubic of the amplitude fluctuation. The ratio is proportional to the square of the amplitude fluctuation and is proportional to the product of the frequency fluctuation and the amplitude fluctuation. Finally, the method of calculating line loss by least squares polynomial fitting technique is given, and the effectiveness is verified by Simulink model.