A new method for measuring the refra ct ive index of liquid is proposed in this paper.It is based on the real-time holo graphic interferometry.A photorefractive crystal (PRC) is used as the recording medium in the holographic interferometer and a longitudinal displacement betwee n the reconstructed object wavefront and the present object wavefront is produce d by inserting a rectangular cell filled with a liquid sample under test into th e object light beam.The interference fringe pattern formed by these two object w avefronts is used as the measure of the refractive index of the liquid sample.Be casuse of using a PRC as the recording medium all the measurements are in situ,i .e.no chemical or physical processing is needed.The system configuration and the principle of the present method are analyzed,and some experimental results are given.The experimental results show that this method is simple,rapid and of suff icient precision.