A full field phase detection system for surface plasmon resonance (SPR) bio-sensor is presented. The phase difference variation between s and p polarization resulting from the SPR was detected by the polarization interferometry. In the polarization interferometry, the light reflected from the SPR sensor was divided into four phase quardrature parts by polarization components. By means of an algorithm similar to phase shifting interferometry, the phase distribution of SPR bio-sensor was obtained. We have successfully detected the phase difference variation with 0.07º resolution within 1×1 mm2 full field range. The corresponding detection limit of the refractive index change is about 1×10-7.