Abstract: Abstract: Under the background of the global energy interconnection, the half-wavelength transmission technology has attracted attention with its huge economic and technological advantages. As more and more renewable energy sources are connected to the power grid, the harmonic problem has become increasingly prominent. On the one hand, it is possible to have a colossal impact on the insulation of electrical equipment. On the other hand, the potential harmonic amplification may affect the stability of the transmission system. However, there are few researches on the harmonic transmission issues of the half-wavelength transmission line, so it is necessary to study it, in order to provide theoretical support for the half-wavelength transmission technology. 1. Half-wavelength transmission line simulation model and correctness verification Due to the complex electromagnetic coupling relationship of the transmission line, its related parameters will change with the change of the current frequency and affect the corresponding electromagnetic transient process. Therefore, for the problem which requires consideration of higher harmonics, it is necessary to optimize the existing line model and use the transmission line model which can reflect all the frequency parameters of the line. Figure 1 shows the equivalent circuit diagram of the frequency dependent model used in this paper. Based on the existing half-wavelength transmission line model, the simulation model was improved by using the frequency dependent model. The structure of the half-wavelength transmission line is shown in Figure 2. The voltage at the head and the end was measured under normal operation. Figure 3 shows the result. 2. Analysis of harmonic transmission characteristics under standard line length The 3rd, 5th, 7th, 11th, and 13th harmonics are the harmonics which needs to be considered in the power system. Taking the 3rd, 5th, and 7th harmonics as examples (the harmonic content is 1%), this paper analyzes the harmonic transmission characteristics of the half-wavelength transmission line with standard line lengths. Figure 4 shows the voltage comparison between the head and the end when the three harmonics are put into the system. On this basis, taking the inter-harmonics which exists between the third harmonic and the fourth harmonic as examples, the transmission characteristics of inter-harmonics were analyzed. The simulation results are presented in Figure 5. 3. Analysis of harmonic transmission characteristics under non-standard line length Because the length of line is difficult to meet 3000km in actual project, it is necessary to study the harmonic transmission characteristics of non-standard line length. In the same way as the second part, the 3rd, 5th, and 7th harmonics are selected for analysis. The relationship between each harmonic transmission amplification and line length is shown in Figure 6. 4. Conclusion The simulation results show that the improved transmission line model can accurately reflect the operation characteristics of the half-wavelength transmission line. It is also suitable for the analysis of harmonic transmission characteristics. Under the standard line length, there is no obvious amplification after transmission of the higher harmonics through the half-wavelength line. However, some inter-harmonics will show obvious amplification after transmission through standard lines. Under the non-standard line length, the amplification of harmonics is closely linked to the length of the line. With the increase of line length, the amplification coefficient of harmonics presents cyclic variation, but the amplification is gradually reduced. Therefore, it is necessary to avoid these problems through manual tuning or parameter setting in practical projects.