We present a heterodyne optical phase-lock loop system for atom interferometers. The frequency and phase synchronization of two external cavity semiconductor lasers are realized. The laser beat signal linewidth is less than 1 Hz, the residual phase noise within 10 MHz integral bandwidth is 0.002 rad2, and the phase noise reaches a flat floor of ?100 dBc/Hz in the offset frequency range of 1kHz to 100kHz. We researched the impact on the sensitivity of the atomic measurement. Using the 200ms’ interrogation time, the 30μs’ π Raman pulse duration time and the 1s’ cycle time, we calculated that our system would allow us to reach a sensitivity to acceleration as low as 10μGal?Hz-1/2.