Abstract: A theoretical model was constitued to study the separation of hydrogen isotopes by electrolysis-distillation process, and separation performance of H2/HD was investigated. Enrichment behavior of both electrolysis and distillation was obtained:HDO concentration in electrolysis increased from 2.88×10-4 to 8.35×10-4,HD concentration in reboiler finally reached 0.033. However,as enrichment develped,deuterium extraction efficiency decreased with time and HD concentration along distillation column increased simutaneously.The reflux ratio’s effect on deuterium extraction efficiency was also studied,deuterium extraction efficiency was between 0.9828 and 0.9973 with reflux ratio between 3 and 7.