Based on the principle of the reflection of polarized light, the measurement of refractive index of the medium is achieved. The highly collimated diode laser is incident on the surface of samples. By gradually rotating the sample or changing the angle of incidence of the sample surface, the relation curves of the test samples′ reflected light intensity versus the incident angle is obtained. When p polarized light is used, there is an incident angle at which the changing rate of the curve approaches zero. The corresponding angle of incidence is called the Brewster angle. According to the principle of the reflection of polarized light, the sample refractive index can be figured out. We use this method to measure the refractive in dices of glass sample and a prism. The deviation of measurement result is at the order of magnitude of 1×10-3, and the measurement repeatability is pretty good.