A new interferometric technique for measuring liquid refractive index (RI) with high accuracy has been developed, which is directly traceable to the wavelength of He-Ne laser. The accuracy of this method is improved by increasing the optical path of step. The experiment revealed that the temperature distribution nonuniformity in the liquid limits the practical uncertainty of liquid RI measurement from 1×10-6 to 4×10-5 (2σ) depending on its temperature coefficient although much finer resolution can be easily achieved with this method.