The strength of forced convection currents, as well as the remixing effect in a continuous-flow thermal diffusion column for recovery of deuterium from H-D gas mixture, can be reduced by employing the device of branch columns, instead of the device of single column, with the same total column length. The improvement in separation increases when the flow rate or the total column length increases. It is found that the improvement in recovery can reach about 50% for the numerical example given.