Reliable power supply has always been the key factor which restricts the wide-range application of on-line monitoring devices on power transmission lines. To address this problem, a novel capacitive power transfer (CPT) system based on resonance coupling is proposed in this paper. By utilizing the transmission lines and the earth, whose potentials are robust, a virtual return route is established, and the conventional four-plate coupling structure is simplified to two-plate structure. Moreover, by using the fringe effect of the charge distribution on coupling plates, the full-area coupling plate is further simplified to annular air-core plate, which is more compact and more resistant to outdoor wind forces. The equivalent circuit model of the proposed CPT system is established, and the detailed system performance is analyzed. Several groups of experiments are conducted to verify the effectiveness of the proposed system structure as well as the circuit model. Both analytical and experimental results indicate that efficient wireless power transfer can be realized using the simplified system structure, and higher transfer efficiency and larger transfer gap can also be achieved when compared with conventional four-plate CPT systems.