By means of first-principles calculating the formation enthalpy, binding energy and states density of γ′-Ni3Al and γ″-Ni3Nb phases, the influence of Nb doping on alloying behaviors of γ′-Ni3Al and γ″-Ni3Nb phases is investigated. Results showed that, in the molten of the γ′-Ni3Al and γ″-Ni3Nb phases, compared to γ″-Ni3Nb phase, the γ′-Ni3Al phase has a lower stability in the range of Nb doping quantity being less than 15.625(at%), but the γ″-Ni3Nb phase has a bigger stability in the range of the Nb doping quantity being more than 18.75(at%). Wherein, the γ′-Ni3Al and γ″-Ni3Nb phases have the close lattice parameters in the range of 15.452-16.34 (at%) of Nb doping, which is thought to be an essential condition of promoting γ′-Ni3Al → γ″-Ni3Nb coherent phases transformation. The difference of the states density in the Femi-level location increases obvious as the quantity of Nb doping is more than 18.75(at%), which enhances the stability of γ″-Ni3Nb phase. Moreover, the decomposition of the γ′-Ni3Al phase occurs at the same time the γ″-Ni3Nb phase growing, which may result in the disappearing of γ′-Ni3Al phase.