Based on the analysis of the recording and reconstructing of hologram and the point spread function of pre-magnification digital micro-holographic system (PMDMHS), the performances of the six common PMDMHSs are compared in imaging resolution, imaging quality and conveniences, for the first time to our knowledge. The results show that the digital image-plane holography (DIPH) has the highest imaging resolution and the best imaging quality; the resolution of DIPH is independent of the photosensitive surface size of the recording device; this system can completely record the information about the object transmitted through the micro-objective (MO); it is not needed to consider the size of illuminated region of object. Moreover, the reconstruction process of DIPH is very simple. DIPH is an optimized digital holographic imaging system. The DIPH with equal curvature of reference wavefront and object wavefront is very conducive to phase unwrapping and phase aberration compensation; therefore DIPH is more suitable for phase microscopy. The experimental results demonstrate the validation of the theoretical analysis.