Superresolution technique is well known for the ability of compressing the central diffraction spot beyond the classic diffraction limit, and it has a wide application in the optical storage and the confocal imaging systems. The radial birefringent filter which consists of two parallel polarizers and a rotationally symmetric birefringent element is introduced into the superresolution technology, and with Jones calculus the pupil function of it is deduced. It is shown that with such filter transverse or axial superresolution can be realized just by changing the angle between the polarizers and the radial birefringent element. At the same time, the superresolution parameters G, Strehl ratio S and the influence of side-lobes are discussed. Advantages of such filter are that it is relatively simple to construct as it requires no phase changes with low cost. Disadvantage is its high strength of the side-lobes, but that can be suppressed by applying confocal system.