Solidification process of aluminum alloy was simulated by a macro-micro coupled model.The model coupled the finite differential method and cellular automaton method.Different from conventional cellular automaton model

the model considered not only temperature field diffusion but also solute diffusion in liquid and solid state as well as curvature undercooling.The relationship between the dendrite tip growth velocity and local undercooling were calculated based on KGT（Kurz-Giovanola-Trivedi） model

and temperature field and solute filed were calculated by FDM.In the macro-micro model

two kinds of grids were adopted to calculate macro-temperature field and microstructure evolution

greatly improving calculation efficiency.Micro-grain growth in the aluminum alloy and solidification of the alloy in permanent mold were simulated by the model

obtaining typical morphology of columnar grain transformed into equiaxed one in the alloy at three kinds of pouring temperatures.