The models of temperature fields and phase transformation of Al-Cu alloy were developed for its near liquidus semi-continuous casting by a multi-scale simulation method，where the change in, solid fraction is available to couple the macro-scale simulation with meso-scale one．The solidifying process of Al- Cu alloys of Cu content of 4％, 4.5% and 5% was simulated during near-liquidus casting at by using finite difference method and cellular automata method at pouring temperature of 7~25 K higher than liquidus temperature, casting speed of 1.5~3.5 mm/s and cooling coefficient of 1 000~2 000 W/（m2•K）. The result is consistent with experimental. the content of alloying elements has great influence on the semisolid microstructure formation．The calculation results showe that microstructure are fine, uniform and near globular when the mass fraction of Cu is 5％, pouring temperature is 930 K, cooling coefficient is 1 000 W/(m2•K) and casting speed is 2 mm/s．