A new structure of tunable polarization interference dense wavelength division multiplexing (DWDM) filter based on the analog birefringent module is presented. It is composed of several cascaded analog birefringent modules with the same structure located between two polarizing devices. Each analog birefringent module consists of a pair of birefringent plates for splitting and combination, respectively, and in between a set of two medium plates of different indices of refraction and one half-wave plate. The center-frequency tunability characteristic of the filter is investigated as well. Results show that as a definite flattening requirement is satisfied, the passband and stopband with wide flatness width and high isolation can be obtained and the center frequency tunability can be accomplished simultaneously when slightly rotating the analog birefringent module unit. The feasibility of the analog birefringent structure is verified through an experiment.