The operation mode of the locomotive micro-devices is a combination of moving forwards, backwards, staying and rotation. In order to supply power by inductively wireless transmission to locomotive micro-devices, the micro-power receiver is often attached with the locomotive device. The distance and orientation between micro-power receiver and magnetic flux transmitter are changed as the locomotive micro-devices operate, rotate or move so that the power received by the micro-power receiver is varying. In this paper, the variable power control is applied on the magnetic flux transmitter to regulate the wireless received power at micro-power receiver. By Biot-Savart law and Faraday's law, the mathematical description from transmitter to micro-power receiver is constructed. By employing commercial software, Ansoft Maxwell, based on finite element method, the estimation error on power transmission by mathematical description is revealed. Besides, the design parameters of micro-receiver and transmitter are also examined for later-on fabrication and set-up. Finally, the test rig of variable power control is also established for performance verification.