Reflection coefficient of the active device is the main parameter which directly affects the output power of the signal. The two methods－impedance tuner and Vector Network Analyzer(VNA) frequency shift , are analyzed in order to measure the reflection coefficient of active device on the state of "RF ON". Some measurement experiments on the signal generator and amplifier are performed. The results show that, the difference between the two methods is less than 0.06，and the phase difference is below 10°, under 10 dBm of the output. The work provides feasible ways to measure the reflection coefficient of active devices.