Wireless power transfer (WPT) enables contactless power transfer from the power supplier side coil (Tx) to the receiver side coil (Rx), which has a wide range of applications. However, for a horizontal randomly moving Rx, the high power transfer efficiency (PTE) cannot be guaranteed as the relative distance between Tx and Rx affects the value of PTE. In this paper, we designed a 4-layer Tx array with Rx tracking algorithm to track the position of Rx and active the Tx at that position in the array. Therefore, the maximal and stable PTE could be achieved for a freely moving Rx, which has been successfully validated in a simulation experiment.