Abstract: The high performance DDS chip AD9858 produced by Analog Device Inc is adopted to design a frequency synthesizer in this paper. A design scheme of DDS +DSP +SAWO is adopted. The designed synthesizer has low phase noise and high stability SAW oscillator to offer a reference clock for AD9858. The whole system adopts high-performance DSP as the control circuit .The main performance characteristics of AD9858 chip and its application to frequency synthesizer with fast frequency hopping is mainly introduced in detail.