This article proposes a segment-switching method of a three-phase wireless power transmitter for automatic guided vehicles (AGV). The method includes the segmented coil structure, the segment-switching control, and circuit configuration with resonant devices. The segmented coil structure ensures that mutual inductance between the transmitter phase coils and the receiver coil is in a three-phase balance. The segment-switching is conducted in each phase; depending on the receiver coil position, the segment of each phase is changed independently and sequentially. The mutual inductances between the transmitter phase coils vary significantly depending on the switching state. The proposed circuit configuration has resonant devices to cancel the variable mutual inductances for effective operation. The receiver position is estimated by the unbalanced current control. Experiments confirm that the method can perform a power transfer of 300W with a slight variation to a moving AGV, equipping the receiver at 30m/min as well as an AGV at a standstill.