Refraction index is one of the most important parameters in investigating the thermal effect of liquid laser. Interferometer technique is one of the most common types of the refraction index measurement, but it is sensitive to disturbances. An experimental method for the refraction index measurement of transparent liquid is presented, based on the single-element interferometer. The interference pattern is captured by a CCD camera. The method is simple as well as stable, which can be easily interpreted geometrically. The accuracy of the refractive index measurement is of the order of 10-4.Compared to the Michelson interferometer, it replies that the stability of the single-element interferometer is better than the typical interferometer′s.