The cold atom interference experiment involves complex laser modulation technology. It’s important to provide a suitable RF drive signal for the modulator. The phase noise of the signal directly affects the sensitivity of the cold atom interferometer. In order to meet the needs, a low phase noise signal source capable of generating 6.834 GHz signal is introduced in this paper. The signal source adopts two-stage phase-locked loop frequency synthesis technology to multiply the 10 MHz signal output by the constant temperature crystal oscillator to 100 MHz, and then multiply the 100 MHz signal to 7 GHz. Finally the 7 GHz signal is mixed with a 166 MHz signal generated by the external DDS chip. A 6.834 GHz signal source is realized. The test result of phase noise is-61.9 dBc/Hz@1 Hz. It meets the needs of cold atom interference experiments.