Abstract: Measurement method of H/D isotope analysis was established through our studying H₂ /H₂O(l) equilibrium by Gasbench-IRMS. By performing a large amount of experiments and measuring standard sample（GWB 04403）， it’s showed that the method owned satisfactory, precision and accuracy. And then the method was applied to measure the local drinking water. In addition, the experiment working standard of H₂ was certified by H₂ /H₂O(l) equlibrium H/D isotope analysis associating with hydrogen isotope fractionation equilibrium equation in H₂/H₂O(l), the result was agreed with chromium reduction method.