In order to overcome the drawback of the conventional pupil filters and realize the tunable superresolution of the optical system, a new type of tunable pure phase filter composed of a half-wave plate located between two quarter-wave plates is presented in this paper, in which the half-wave plate is made of two zones. The simulation results show that with such a pupil filter the tunable transverse superresolution as well as the axial extended focal depth of the optical system can be realized by rotating any zone of the half-wave plate.