In this paper the reflection detection of second harmonic from a 915-MHz radio-frequency (RF) energy harvesting prototype system is demonstrated. The prototype system contains an RF power emitter and a power receiver. The power receiver is composed of a rectenna and a commercial power management demoboard. The power emitter includes two commercial software-defined radio (SDR) transceivers to act as a RF power radiator and a harmonic detector for energy harvesting and harmonic reflection detection, respectively. From the experimental results, the transmission power of about +18 dBm are delivered to the rectenna to start up the power management demo board to hunting electrical energy at a distance of 50 cm. By directly reading the measured harmonic power strength with a SDR tool, a detectable harmonic power level difference can be observed. The difference over 10 dB can be obtained. Thus, it can be used as an index signal to identify the directional position of the power receiver.