Distributed parameters characteristics of long-distance transmission lines are easy to cause（inter） harmonic amplification.We propose a method for analyzing frequency characteristics of lossy half-wavelength AC transmission lines based on the frequency-length factor in order to analyze the（inter） harmonic transmission characteristics of half wavelength transmission lines.An equivalent（inter） harmonic transmission calculation model of lossy transmission line which takes the product of frequency and line length as a variable is built through successive simplification.Based on the calculation model

the amplification rules of the end harmonic voltage caused by the injected harmonic voltage were determined.The characteristics of poles distribution of frequency-length factor are also studied to find the resonant frequency.The envelopes of the resonance amplitude are calculated so as to determine the critical condition of the inter harmonics.Moreover

in order to determine the（inter） harmonic voltage amplification at the remote end caused by the injected（inter） harmonic current at the sending end of a lossy half-wavelength AC transmission line

a method to analyze the（inter） harmonic voltage amplification based on the reference impedance is proposed.It proves that the harmonic voltage or current source which is injected into the sending end of the lossy half-wavelength transmission line does not produce the harmonic voltage amplification at the remote end considering any system operation mode

and the problem of resonance occurs in some inter harmonics.When the line loss and load condition meet the criteria of no amplification

the inter harmonics will not be enlarged

otherwise

some of them will be enlarged.Calculation errors between the PSCAD simulation and the model calculation are less than 2%

which proves the correctness of the model.