In the atomic gravity measurement experiments, the linear chirp of the master and slave Raman lasers is achieved by a swept frequency source, which in turn compensates for the Doppler frequency shift produced by the atoms during free fall, thus enabling the measurement of the local gravitational acceleration g. Aiming at the problems of large volume and large heat generation of the traditional sweptfrequency source, this paper uses the AD9959 digital chip to implement a swept frequency source, which can be used as an atomic fountain frequency sweeping control and Raman optical phase-locked loop discriminating frequency and phase local oscillation reference. The final experiment shows that the phase noise of the swept frequency source is -112 dB@1 kHz, and the frequency stability is 1.38×10^-11@1 s. The effect on the sensitivity of the atom gravimeter is 2.81×10^-9 g/Hz^1/2, and the effect on the atomic gravimeter experiment is 1.15×10^-10 g within 600 s integration time. The system has the characteristics of low noise and high stability, and can meet the 10^-10 g resolution requirement of portable atomic gravimeter. The research results provide a certain reference for the development of atomic gravimeter from the principle prototype to the engineering portable experimental test instrument.