When the magnetic coupling mechanism of the wireless power transfer system is deviated and deflected, there are problems of a drastic decrease in coupling coefficient and efficiency. In this article, a single flux loop grid flat spiral pad (GFSP) magnetic coupling mechanism is designed for medium or small power wireless charging applications. The uniform distribution of the magnetic field makes it both anti-misalignment and anti-deflection. In addition, a single-switch inverter P#LCC-S resonant network topology is proposed for the compensation topology, which effectively simplifies the circuit structure while retaining the performance of the traditional LCC-S compensation network. Firstly, a magnetomotive force model is formulated to reveal the magnetic field distribution law at different spatial positions of the mechanism and optimize the parameters of the mechanism. Secondly, an equivalent model of the dual P # LCC-S resonant network circuit is established to derive the parameter configurations of the resonant elements under the constant excitation current of the transmitting coil and the constant output voltage. Finally, a 300 W experimental prototype is constructed, and the coupling coefficient retention rate of the prototype is always larger than 50% and the transmission efficiency is greater than 80% within the ranges of ±120 mm of XOY plane misalignment, 50 ~ 100 mm of Z-axis misalignment, and 0° ~ 90° of Z-axis deflection, respectively. Therefore, the validity and feasibility of the proposed system are evaluated.