In order to solve power supply problems of online monitoring equipment on the tower side of 110 kV transmission line, a novel U-shaped high-voltage wireless power transfer (WPT) system based on vertical relay coil is proposed in this paper. With mutual inductance coupling theories and finite element simulations, an overview design of the proposed WPT system is given. The WPT system provides a promising power supply method with longer distance, larger power, higher efficiency, and broader band to online monitoring equipment on the tower side. On this basis, a systematic simulation model is established for detailed analysis of characteristics on the distance, frequency, load resistance and electromagnetic distribution of the U-shaped WPT system, and the feasibility and electromagnetic compatibility of the proposed design scheme is verified. Finally, an experimental platform is built. The output power of the proposed system is demonstrated to reach 73.58 W respectively with 600 kHz frequency and 1.2 m distance, which completely meets practical power requirements of the online monitoring equipment on the tower side. This paper can be seen as a reference for the application of wireless power transfer technology in the field of high voltage equipment power supply.