According to optical imaging theory and the point spread function of digital holographic system, the imaging resolution of the digital holographic microscopy was investigated. The imaging resolution expressions of the digital holographic systems with and without pre-magnification were presented in details. With those formulas, it is clearly shown that only when the imaging resolution of CCD is not below the resolution of the microscope objective (MO), the imaging resolution of the whole system is dependent on the numerical aperture (NA) of MO. Otherwise, it is dependent on the numerical aperture of the CCD. Experimental imaging of US air force-resolution test target is performed using the lensless Fourier transform configuration. The experimental results that ultimate resolution of reconstructed image in horizontal direction and vertical direction is 3.91 μm and 4.38 μm respectively. Finally, recording and reconstructing of holograms for stripe object are stimulated , and results are corresponding with theoretical analysis.