The power line is designed for the electricity transmission. The complicated distribution network topology induces the deteriorated communication channel and complex channel characteristics of the power line, which deteriorates the quality and efficiency of the signal transmission. To deal with the above problems, the mathematical model of the power line channel is established by utilizing the twoport network of the transmission line. Based on the model, it is simulated and analyzed that the influence of the power network structure and network parameters on magnitudefrequency characteristics of the channel voltage and network input impedance. It is found that in the magnitudefrequency characteristics, the peak and valley positions have a low correlation with the length of the main line, and the number of the peak and valley has a high correlation with the length of the branch line. Besides, the input impedance of the network is equal at the peak frequency.