In order to improve the resolution of confocal scanning microscope system, three-zone annular binary pure phase filter is designed with the vector diffraction theory. When the high numerical aperture focused 1.4, the light intensity distribution near the focus is numerical simulated. Based on the Strehl ratio and axial resolution, the structures of the three-zone annular binary pure phase filter which achieved optical superresolution could obtained with the optimal search algorithm. The simulation results show that axial superresolution and low side-lobes can be realized with the designed three-zone annular binary phase filter in the confocal scanning microscope systems and other high numerical aperture system.