Abstract: Base on the kinetics of the dendritic tip growth and least energy of grain growth theory,a two-dimension CAMC (Cellularautomata-Monte Carlo) grain growth mathematical model for weld pool which couples macroscopic heat transfer with microscopic solute transfer,nucleation and growth is developed.The skeleton of grain is formed by using CA model,and then the growth of grain is corrected by MC model.In the model,the mechanism and influencing factors of heterogeneous nucleation,which occurs at the boundary of welding zone,are taken into account.The dynamic process of microstructure formation in welding zone is presented.The evolution of amount,dimension and appearance of grains can be described quantitatively by using CAMC model,and the choosing growth of grain and the transition from columnar to equiaxed crystal can be exhibited by model.It is successful to simulate the microstructure evolvement during metal solidification of welding zone by CAMC model.