Multi-coil wireless power transfer (WPT) for power supply applications in high-voltage transmission line monitoring equipment faces insulation issues caused by excessive electric field concentration. This paper proposes a novel WPT system based on a domino resonator structure. A mathematical model of the multi-coil WPT system is established, and an expression for the output power efficiency of the multi-coil coupled WPT system is derived. Based on this, 3D finite element electric field simulations are conducted, showing that the proposed embedded resonator exhibits superior insulation performance, with improved electric field concentration in the insulator after the resonator is added. High-voltage experiments are performed in a high-voltage laboratory, where the proposed domino embedded resonator WPT system is subjected to voltages up to 252 kV, and the system operates normally. Both simulation and experimental results demonstrate that the proposed solution can meet the power supply requirements for online monitoring equipment on 220 kV high-voltage transmission lines.