In order to obtain the output of dual-frequency laser with large frequency difference, a new birefringent filter consisting of a polarizing beam splitter and a half wave-plate has been designed as a laser longitudinal mode selector. When the birefringent filter is included in a laser-diode(LD)-pumped Nd:YAG laser cavity, the laser is enforced to oscillate in single longitudinal mode. When the angle between the fast axis of the half wave-plate and the polarizing plane of the polarizing beam splitter is changed by rotating the half wave-plate around the laser cavity axis, the output power of the single axial mode laser varies periodically with a period of approximately π/2. A LD-pumped two-cavity dual-frequency Nd:YAG laser with large frequency difference has been designed and experimentally investigated, which has both straight and right angle standing-wave cavities sharing the same gain medium and the longitudinal mode selector. The p-and s-component of 1064 nm laser light oscillate simultaneously in single longitudinal mode in the straight and right angle cavities, respectively. The resonant frequency of the single longitudinal mode oscillated in each resonant cavity can be tuned by changing each cavity-length so that the frequency difference of the dual-frequency laser is tuned. It has been observed experimentally that the frequency difference of the orthogonally and linearly polarized dual-frequency laser at 1064 nm is tunable in a range from 27 to 113.4 GHz.