The aqueous two phase region and polarizing regions of sodium dodecyle sulphate (SDS) cetyl trimethyl ammonium bromide (CTAB) H 2O have been determined on a pseudo ternary phase diagram, and the influence of added salt NaBr on them has been observed. It is shown that there are two ATPSs in the aqueous solution of SDS and CTAB mixture, one of them has the cloud point. The upper phase of ATPS is liquid crystal and the lower phase isotropic solution. The added salt NaBr can change the composition of ATPS regions and the polarizing regions. When the salt concentration increases, the position of ATPS region will move to higher concentration of SDS and CTAB. If the concentration of NaBr is higher than 0.2mol/L, the ATPS regions will partly overlapped the polarizing regions and the polarizing phenomenon in the upper phase of some ATPSs will disappear.