A rigorous thermodynamic model was used to study the characteristics of cryogenic distillation column of hydrogen isotope system having feedback stream. The steady-state behavior was studied establishing a fundamentally sound model that is capable of accurately describing the separation process. The numerical algorithm which can provide better stability，accuracy and efficiency in computing time was developed to solve complex cryogenic distillation problems. A side stream was sent to an equilibrator as an internal feed stream and then mixed with the external feed stream of the column. The simulation results indicated the effects on the characteristics of cryogenic distillation column. The feedback stream was partly decomposed at the equilibrator into H2 and D2. Mole fraction of H2 in the top product increased by 8.635%

and mole fraction of D2 in the bottom product increased by 11.327%.