Abstract：To tackle the issues of oversize and inconvenient wearing of the conventional wrap-around-style transmitting coil, in this paper, a new wireless power transfer (WPT) system is proposed for capsule robots. The key is to use a planar spiral coil as the transmitting coil, which effectively reduces the size of the transmitting coil. As a result, the inconvenient wearing issue is avoided and the capsule robot-oriented WPT system becomes more adaptive. First, the equivalent circuit model is established, based on which several parameters are investigated as the influencing factors of the transfer efficiency. Then, the turns of the receiving coil are optimized to promote the efficiency. After that, the equivalent load resistance is optimized with an impedance converter. Finally, several experiments are carried out to verify the feasibility of the proposed system. As a result, an overall efficiency of 8.8% is realized at 10-cm distance with the output power larger than 1 W. In addition, the optimized coil can be extended to three-dimensional transmitting system.