Abstract: The Nd∶YAG microchip laser with orthogonal linear polarized dual-frequency output was designed. Two quarter-wave plates in which one is static, another rotates around in 360°, are set in the laser cavity. The intra-cavity variable birefringence caused by relative rotation of two wave plates in laser cavity results in changeable frequency difference of dual frequency. Thus, the output of the tunable dual-frequency laser is realized. The eigen-mode of laser in the cavity was analyzed with Jones matrix. The theoretical description for the frequency diversity of dual-frequency is presented. The potential laser goniometer with small volume, high resolution and ability of precision 360°measurement is discussed.