The distributed optical fiber sensors can measure the environment factors which continuously distributed along a length of optical fiber. For a distributed fiber sensor taking a polarization-maintaining fiber as sensing fiber, the environment factors induce the orthogonal polarization modes propagated in the fiber coupling each other. The sensing signal is detected by means of compensating the optical path difference of the two orthogonal polarization modes by two arms path difference of Michelson interferometer. In order to design white light interference distributed optical fiber sensor by polarized modes coupling, the mutual coherent characteristics of the sensor were analyzed according to the principle of statistic optics. On these bases, the length resolution, fiber coupling point resolution and maximum sensing fiber spatial of the sensor were obtained. The length resolution and the coupling point resolution are 6 cm and 3 mm respectively for a distributed optical fiber sensor with a superradiant light-emitted diode(SLD) source of center wavelength 1310 nm, spectral width 36 nm and a polarization-maintaining fiber of polarization dispersion coefficient 600 ps/km and beat length 3 mm.