The digital image-plane holographic microscopy which has the same curvature radius in the object light path and the reference light path is studied for the first time to our knowledge. The configuration of this setup is analyzed and built. The point spread function of this system is derived. The factors corresponding to the imaging resolution and the imaging characteristics of this system are analyzed. The method to correct the linear phase distortion in the reconstructed optical field is discussed. The results show that this system has the largest information content, and the imaging resolution of the system is dependent on the numerical aperture of the microscope objective (MO) and on the CCD pixel size, but independent of the photosensitive surface size of the CCD. All frequency components of each point in the object wave which has passed through the MO can completely be recorded and reconstructed. And the size of illuminated region of object has no influence on the recording condition and the quality of the reconstructed image. The digital image-plane holographic microscopy with the same curvature radius in the object light path and the reference light path is an optimized holographic recording system, which can achieve high-quality imaging. The experimental results demonstrate the correctness of the theoretical analysis.