Cu-Co alloys demonstrate immense potential for industrial applications due to their excellent properties, including high electrical conductivity and giant magnetoresistance effect. As typical immiscible alloys, Cu-Co alloys are prone to liquid-phase separation during their preparation; as a result, their components undergo severe segregation, limiting their applicability. Thus, investigating and elucidating the evolution mechanism of solidification structures of the Cu-Co alloys is imperative. However, liquid-phase separation in these alloys occurs on miniscule time and space scales, and complex physical processes such as diffusion, convection, and heat transfer are also involved. Hence, investigating the kinetic characteristics of alloy solidification and the mechanisms of microstructure formation solely by experimental methods using the existing technology is challenging. Nevertheless, with the continuous advancement of theoretical foundations and computational capabilities of materials, numerical simulations have emerged as an effective tool for investigating the microstructure evolution of immiscible alloys. This study investigates the mechanisms involved in the formation of core-shell structures during the solidification of Cu-Co alloys using a combination of experimental and numerical simulation techniques. Based on the phase-field method, three parallel simulations, incorporating fluid flow and Marangoni motion, were conducted. The microstructure evolution at various stages and under different conditions was systematically analyzed. The simulation results indicated that the fluid flow resulting from liquid-phase separation could expedite the coarsening of the second-phase droplets. Furthermore, Marangoni motion driven by temperature gradients resulted in the coalescence of second-phase droplets at the center (high temperatures), accelerating the coarsening process. The Ostwald ripening phenomenon and coagulation process between the second-phase droplets were simulated, and the growth kinetic mechanisms of the second phase were revealed. In addition, three Cu-Co alloys were used for simulations to investigate the impact of the volume fraction of Co-rich phase on the microstructure evolution. The validity of the simulation results was confirmed by comparing the simulated solidification structures with those obtained experimentally.