Abstract: A coupled model of cellular automaton and finite difference was established and applied to solidification process in molten pool of nickel base alloy.The growth of various solidification microstructures,including planar crystal,cellular crystal,columnar dendritic crystal and crystal equiaxed dendritic in molten pool was firstly carried out and contrasted with experiment results.Moreover,variation in solidification mode in molten pool was performed,which represented cellular-to-dendritic and columnar-to-equiaxed transitions.The effect of diffusion on the distribution of solute was also calculated by solute diffusion model.The simulation results were in good accordance with the experiment results.