A thermodynamics/dynamics coupling analysis method is proposed based on CALPHAD/MD methods. The microstructure evolution of the Cu-24Pb-xAl immiscible alloys is deeply investigated under both equilibrium and non-equilibrium solidification using this method. The influence of Al content on the morphology evolution of the secondary phases in the Cu-24Pb-xAl alloys is revealed by comparing experiments and the coupling analysis method. Increasing Al content in the Cu-24Pb-xAl alloys promotes the transformation of secondary phases from a continuous network to a granular morphology by intensifying the segregation of Pb atoms and the liquid–liquid phase separation. The phase transformation process is investigated in situ. The calculation results based on this method present a high degree of compatibility with the experiments which present a solidification rate higher than that of CALPHAD and lower than that of MD. The combination of CALPHAD and MD contributes to the establishment of a multiscale research method for the solidification of alloys. Simultaneously, the coupling analysis method is universal and will provide guidance for the composition design and microstructure regulation of new immiscible alloys.