Wave trapper is not allowed to install in medium voltage distribution network, so the signal of power line communication (PLC) will be distributed through the substation bus into various lines. Firstly, the measured data of substation signal shunt is given. Then the model of PLC network is builded, and the influence of signal distribution on the channel characteristics is analyzed. It is found that power transmission characteristics can reflect PLC channel quality more accurately than voltage transmission characteristics under the influence of substation signal shunting. Finally, under the condition that the communication distance is affected by signal shunting, the influence of the main node position on PLC network structure is simulated and analyzed based on the hierarchical search networking algorithm. The simulation results show that setting the main node of the PLC network on the middle of the line can increase the communication range and reduce the number of network layers, so as to weaken the negative influence of the substation signal shunting.