The dual-focus interference microscope is applied in various areas because of its characteristics of high stability and resolution. The birefringent lens, consisting of a piece of birefringent crystal and a piece of optical glass, is a key component in the dual-focus interference microscope. In order to design the birefringent lens easily and promptly, not only the concept of “pseudo-chromatic aberration” introduced but also “the reciprocal of pseudo-chromatic dispersion” is defined. Thereby, with the use of the primary aberration theory and the PW method, a useful table of the primary structure of the birefringent lens is given, with the couple of three kinds of birefringent crystals and optical glasses, according to different demands; the calculation of aberration and optimum design are carried out by OSLO, an optical software, and the desired result is obtained. For the sake of evaluating the specific structure, the compact factor γ is defined as a criteria. As a concrete example, calcite and ZF1 are used as materials, the compact factor γ is 0.25.