An optical frequency synthesizer can output single-frequency Hz-linewidth laser with high frequency stability at a specified optical frequency within a wide spectral range. Based on a prototype of optical frequency synthesizer at 700-990 nm, we make a step towards its automatic control. The wavelength of output laser and a motorized rotation stage of a grating are set automatically after comparing the reading of a wavemeter with the target output frequency. The beat frequency signal between the output laser and femtosecond optical comb can be obtained, and automatic signal processing can be realized, obtaining phase-locked control signal between the output laser and reference laser. An error signal for laser frequency control can be obtained within one minute. This study lays a foundation for the realizing the fully automatic optical frequency synthesizer.