A novel unattached laser feedback interferometer by combining the laser feedback effect with the frequency splitting technology is presented and demonstrated. Light source is the birefringence dual frequency He Ne laser which generates o-light and e-light with orthogonally polarized states. When the feedback mirror is moved along the laser axis, the intensity of both o-light and e-light is changed periodically. If a threshold intensity for the output light is appropriately given by the signal processing circuits, the remaining intensity curves in each period shows four different polarization states: e-light, e-light and o-light, o-light, and no-light. Each change of polarization state corresponds to λ/8 displacement of the feedback mirror. We determine the movement direction by the difference of the order of the polarization state appearance. The resolution of the system is 0.079µm. In the experiment, the reflectivity of feedback has no influence on waveform. The laser feedback interferometer is likely to become an instrument which has no real contact with a measured object.