Abstract: In order to improve the resolution of digital holographic imaging system, the recording and reconstruction processes of a pre-magnification digital holographic system with a spherical reference wave are theoretically deduced. Then the point spread function is obtained and the factors to determine the imaging resolution of this system are analyzed. In the case of the CCD imaging resolution higher than that of the microscope objective, the relationship between the resolution and the recording distance of the system is discussed through the experiment of resolution target USAF. The result show that the resolution of reconstructed images is not sensitive to the recording distance. But as the recording distance is zero, which is named digital image-plane holography, the resolution of reconstructed images is highest. The experimental results are consistent with the theoretical analysis.