Based on the Karma thin interface phase-field model which include the solid diffusivity, the effects of interface width and thermal noise on the dendrite growth behavior in undercooled melt of Al-Si alloy were studied by using three-dimensional adaptive meshing method. The simulation results show that with the increase of interface width, the complexity of dendrite morphology decreases, the dendritic tip velocity decreases and the solute concentration at the tip liquid phase decreases. With the increase of thermal noise amplitude, the dendritic tip changes small, the number and asymmetry of secondary dendrites located on both sides of the dendrite increases.