Hydrothermal diamond-anvil cell and Raman spectrograph were used to measure the hydrogen isotope fractionation factor between benzene and heavy water at high P-T condition. The isotope fractionation factor is determined when the isotope fractionation between phases reached equilibrium. This research shows that hydrogen isotope fractionated easily between benezene and water, different from hydrogen isotope fractionation betweenwater and n-alkanes or cycloalkanes. In this study, benzene was dispersed to many small particles, indicating the increasing contacting area to heavy water when temperature reached 300 ℃. Sufficient heating time enabled that stable isotope phases to reach the fractionation equilibrium. The ratio of Raman peak intensities and ratio of corresponding amount of substances is linearly correlated. The calculated hydrogen isotope fractionation factors between benzene and heavy water is 0.909 9 at 300 ℃. Taken together, it is feasible to determine the stable isotope fractionation factor between liquid phases with Hydrothermal Diamond-Anvil Cell combining with Raman spectroscopy.