In the paper, a biochemical sensor based on surface plasmon resonance technology in heterodyne interferometry is proposed. The biochemical sensor is designed as an elongated prism that is made of BK7 glass. The two-sides of the elongated prism was coated with 2nm Ti-film and 45.5nm Au-film. On the basis of surface plasma resonance principles, the proposed biochemical sensor capitalizes on the adhesion activity between test fluids and metal films. Attenuated total reflection occurs when light permeates metal films, resulting in the phase variation. Thus, the fluid properties can be determined by measuring the phase of the exit light. Because adding chemicals or agents to the proposed biosensor is unnecessary, the properties of the measured sample are unaffected during measurements. With the biochemical sensor, the refractive index of the tested medium can be obtained only by measuring the phase difference between the p-and s-polarization lights due to the multiple attenuated total-internal reflections (MATRs) effect. The photoelectric biosensor has a sensitivity of up to 2.6×104 degree/refractive index. Besides, the best resolution of the sensor can reach 3.8× 10-7 refractive index unit (RIU). It also features several advantages such as instantaneous measurement, high sensitivity, simple experimental architecture, and low cost.