Abstract: This paper describes a frequency stabilization system which uses the frequency discriminating method with output energy-input frequency relationship of a resonance cavity. To integrate the output signal from the cavities not only reduces the disturbance from the modulating pulse, but also increases the frequency stability. A high efficiency stepping motor servo subsystem is used, the power of the subsystem is decreased evidently. The stabilized operating frequency of the LINAC is 2856MHz and the unstability of the system is not larger than ± 7 10- 6.