The synthetic aperture algorithm can achieve bidirectional dynamic focusing of ultrasound transmission and reception, thus improving imaging resolution; however, some problems still exist such as low image signal-to-noise ratios (SNRs) and obvious side lobes. To further improve the quality of ultrasound imaging, this study proposes a synthetic aperture ultrasound imaging algorithm called coherence factor and complementary sequences (CFCS) based on coded excitation and coherence factor. First, a pair of Golay complementary sequences are adopted as the excitation signal, and the SNR of the image is increased by increasing the coding length of the transmitted pulse. Simultaneously, the good autocorrelation characteristics of complementary sequences are exploited to eliminate the distance side lobes; thus, the axial resolution of the image is improved. In addition, a coherence factor is introduced to suppress the lateral side lobes in the image. The simulations indicate that, compared with the synthetic aperture algorithm based on Barker coded excitation, the CFCS algorithm can effectively eliminate the distance side lobes; the axial resolution is also improved by 47.4% using the CFCS algorithm. Furthermore, compared with the synthetic aperture algorithm based on coherence factor, the CFCS algorithm's axial resolution and SNR increase by 31% and ~18 dB, respectively.