In order to improve image quality,the point spread functions of practi cal image-plane digital holographic microscopic system (IPDHMS) with both spherical and plane reference waves are derived.The im aging resolution and imaging characteristics are analyzed.The corresponding experimental investigations are conducted.The resul ts show that the imaging resolution of IPDHMS depends on the imaging resolution of the microscopic objective (MO) and the p ixel size,but independent of the photosensitive surface size of the CCD.The big size of the illuminated region of the test sample doesn ′t affect the recording and the numerical reconstruction of the hologram.All frequency components that pass through the MO of each point in the imaging area can be completely recorded and reconstructed.IPDHMS is an optimized holographic imaging system,which can achieve high-quality imaging.The experimental results demonstrate the validity of theoretical analysis.