An indoor lowvoltage powerline carrier communication transmission model is proposed, which is suitable for multi branch topology, multi load impedance in the frequency band of 1~300 MHz. The transfer function is derived from the parameters of the wire material itself and its environment. The model is based on the transmission efficiency of each connection section, than the total transmission efficiency of the system is obtained. According to the measured amplitudefrequency characteristics, the theoretical model is modified to make it possible to simulate the transmission characteristics of different model topologies. The proposed model is helpful in frequency bands preselection for actual power line systems.