A dendritic growth model is established by combining the physical properties of dendritic growth with the characteristics of the cellular automaton (CA) method. The heat process and the molten pool model of the arc-shaped in the process of welding solidification are coupled by using the interpolation method. On the basis of that, the growth of dendrites in the molten pool for Ti-6%Al and Ti-45%Al alloys is simulated and the influence of aluminium content on the morphology of dendrites in the welding solidification process is analysed. And also the microstructural evolution of the molten pool during the solidification process is implemented under the condition of the non-uniform temperature field. The results indicate that the temperature presents the gradual distribution in the non-uniform temperature field and the microstructure grows competitively at the center of the molten pool. During the progress of solidification, the solute atoms are enriched in between dendrite arms with the segregation of solute. Simultaneously, with the change of temperature field, the morphology of dendrites has asymmetry. In addition, the columnar crystals are largely converted to equiaxed crystals for Ti-6%Al alloy while the result is the opposite for Ti-45%Al alloy resulting from the change of the aluminium content. The simulated results are in good agreement with the experimental ones.