Pupil filter is an important optical superresolution element. In fabrication, phase-only pupil filter is more difficult than amplitude-only pupil filter. Diffraction optics can be used to fabricate the phase-only pupil filter, but this pupil filter cannot be tunable. The application of liquid crystal in phase-only pupil filter makes the fabrication easy. But the large decrease of intensity and the limited phase changed depth complicate its use in phase-only pupil filter. A new way to fabricate the phase-only pupil filter with uniaxial crystal is put forward. This phase-only pupil filter can be easily used in application. And there is no distinct decrease of light intensity. By numerical calculation, the feasibility of this design is demonstrated.