Abstract: The 2-D Cellular Automaton model has been established to simulate the solidification microstructure of weld metal. The proberbility necleation of grains, the curvature undercooling, temprature undercooling, constitutional undercooling, latent, the solution redistribution and the expital growth of grain in HAZ has been invoved in the model.The differential method was used to calculate the diffusion of temperature field and concentration field in the uniform grid.The simulations reflect the nature of weld solidification reasonably, whicn shown that the cellular automaton method could be utilized as a new tool for simulating solidification microstructure.