Abstract: The driving power for a Multiple-beam klystron amplifier is critical. By using a Programmable Controller (PLC), a self-adapting control system or equalizer have been designed, which can automatically control the driving power of the amplifier. Based on the output peak power of the klystron, the system automatically controls the driving power of the klystron by adjusting an electric adjusted attenuator. By using this system, the influence caused by variations of signal level, travelling wave tube (TWT) gain, circuit attenuation and klystron characteristics can be dramatically reduced, resulting in that the klystron always works in the best driving state and the biggest output power can be abstained.