A design method of the X band frequency source is introduced in this paper.The synthesizer contains two single loop digital PLL frequency synthesizers,and then mixes them to achieve the X band frequency source,which has lots of characteristics,such as low phase noise,low suprs,and high frequency stability. The test results show that: the phase noise of the frequency source is:-94.3 dBc@1 kHz,-99 dBc@10 kHz; the power level of the output greater than 13 dBm,a good performance frequency source is realized.