The mathematical expressions of synthetic aperture digital holography and phase-shifting synthetic aperture digital holography are presented. Based on the cross-correlation algorithm of both the object waves and the phase-shifting sub-holograms, a high precision synthetic method of the sub-holograms in phase-shifting synthetic aperture digital holography is proposed. Firstly, the position relation of the sub-holograms is determined by the cross-correlation algorithm of the adjacent object waves, then phase-shifting synchronization matching is implemented by the cross-correlation algorithm of the phase-shifting sub-holograms, thus it is convenient to reach the separation of the spatial connection matching of the sub-holograms and phase-shifting synchronization matching of the phase-shifting holograms. By use of the Chinese standard resolution test chart 2# as the experimental sample, the results show that the correlation coefficient of both the sub-holograms connection matching and phase-shifting synchronization are more than 0.99, and the reconstructed image with high quality is obtained.