Taking Ta–W alloy system as an example, the concentration formulae of alloy genes of DO 3 -type alloys in BCC structures were derived on the basis of the theory of alloy genes and the number of coordination atoms. The concentrations of alloy genes of DO 3 -TaW 3 and DO 3 -Ta 3 W ordered alloys were calculated as functions of composition xW and ordering degree (s). When s=smax, the concentrations of alloy genes of stoichiometric DO 3 -TaW 3 compound are equal to those of alloys, that is, x 8 Ta 0.25(at), x 4 W 0.5(at), x 8 W 0.25(at). The concentrations of alloy genes of stoichiometric DO 3 -Ta 3 W compound are also equal to those of alloys, that is, x 0 Ta 0.25(at), x 4 Ta 0.5(at), x 0 W 0.5(at). As ordering degree decreases, alloy genes of DO 3 -TaW 3 and DO 3 -Ta 3 W ordered alloys will split. And the degree of splitting of alloy genes increases with the ordering degree decreasing. The atomic states and properties of DO 3 -TaW 3 and DO 3 -Ta 3 W ordered alloys were calculated as a function of composition xW. The reason was pointed out that preparation of DO 3 -TaW 3 and DO 3 -Ta 3 W intermetallic compounds is difficult due to small differences in their cohesive energies. It will provide theoretical guidance for the scientific designation to new candidate for ultrahigh- temperature materials in areo-engine applications.