Dendritic is the most observed microstructure in metallic materials. Traditional Cellular Automaton model can only predict the grain structure and grain size. It is necessary for us to modify the original model to reflect the real shape of dendrite. In the paper, a mathematical model was established to describe the evolution of the dendritic shape, in which the influence of microsegregation and curvature on undercooling was taking into account. In addition, the growth model was proposed based on the minimum free energy principle. Modeling results indicated the proposed models can predict not only grain structure, but also dendritic morphology. Free growth of equiaxed grains and the competitive growth of columnar grains were simulated. The modeling results were also validated with experiments.