In the neutral point grounding system, in order to suppress the subsynchronous resonance that may occur between the mechanical and electrical systems, a blocking filter is connected between the neutral point of the transformer high voltage winding and the ground. Due to the connection of the blocking filter, the voltage of the transformer’s neutral point to ground changes. Especially when a fault occurs, the surge in the voltage of the transformer’s neutral point may affect the insulation. Based on the actual data of the 500 kV booster station and blocking filter of the Tuoketuo Power Plant, a PSCAD/EMTDC simulation model is established. The simulation discovers the over-voltage law of the blocking filter zero-order reactor at different compensation levels and different ground faults. A method of suppressing the current flowing through the transformer neutral point through a zero-order reactor is proposed, and the zero-order reactor is obtained. The design value of the compensation degree of the filter and the configuration method of the insulation protection of the blocking filter are pointed out.