Abstract: The solidification behavior of Cu_100-XFe_X(X=15, 20, 30 and 40) alloys was investigated by gas atomization. Considering the common action of minority phase spheres' nucleation, diffusion growth, spatial movement and interaction between solidification interface and minority phase spheres, a model was developed to describe the kinetics of metastable liquid-liquid phase transformation and microstructure evolution in the metastable immiscible alloys with different volume fractions of minority phase spheres. Coupled with the movement, thermal and mass transfers during the atomized droplet flight, the numerical model was resolved. The kinetics of metastable liquid-liquid phase transformation in Cu-based immiscible alloys was investigated by numerical simulation. The results indicate that the average size of Fe-rich spheres increases with the increase of Fe concentration. The nucleation event takes place around the peak of matrix liquid supersaturation. With the increase of cooling rate, the nucleation undercooling and the nucleation rate increase, but the average radius of Fe-rich spheres decreases. The formation of Fe-poor layer on the large powder surface is the result of the common actions of the Fe-rich spheres' Marangoni migration and repulsive interaction between the solid/liquid interface and Fe-rich spheres.