;In this thesis, an Analysis and study on a New-type Electro-optical biosensor is proposed. The refractive index of the liquid can be used to measure the biosensor. The biosensor is designed as the polygon prism that is made of BK-7 glass with the refractive index of 1.51509.We used different concentrations of alcohol as a sample. As a heterodyne optical source is launched into the biosensor, the intensity and phase difference between s-and p-polarizations can be obtained. According to Fresnel’s equations and some numerical calculations, the related parameters of the test medium can be obtained. The biosensor has some merits, e.g., a simple optical setup, easy operation, high measurement accuracy, high resolution, high sensitivity, and in real time, etc.