Abstract: The models of temperature fields and phase transformation of Al-Cu alloy were developed for its continuous casting, where the change in solid fraction is available to couple the macro-scale simulation with meso-scale one. The steady state temperature field was calculated by the extrapolated non-physical boundary we proposed in the near liquidus semi-continuous casting process. The average undercooling of the cells in liquid/solid phase transformation region was taken as the principal parameter to calculate the nucleation rate in the melt by virtue of Rappaz's model, thus avoiding the extra estimation of the nucleation of the core of continuous castings. The solidifying process of Al-(3.5-10)wt% Cu alloys was simulated during liquidus casting at a casting speed 2 mm/sec. As a commonly used Al-Cu alloy, the ZL201 alloy was also simulated and the result is consistent with experimental result. The calculation showed that the content of alloying elements has great influence on the semisolid microstructural formation. When the mass fraction of Cu is 8%-10%, a microstructure can be obtained with favorable grain size and its distribution.