A study of heavy water in continuous thermal-diffusion columns on modified Frazier-scheme, resulting in substantial improvement of the separation efficiency of heavy water, was developed and investigated with column length varied at a constant ratio and with flow-rate fraction variations. The analytical results are represented graphically and compared with that in a classical Frazier-scheme of the same column length. Considerable improvement in the enrichment of heavy water was obtained by employing such a modified Frazier-scheme, with column length varied at a constant ratio and with flow-rate fraction variations instead of using a classical Frazier-scheme thermal diffusion column with the same column length. The effect of the ratio of column length and the column number as well as the flow-rate fraction variation on the enhancement of the separation efficiency of heavy water is discussed.