The growth of intermetallics phases between molten aluminium and solid steel was investigated via the imaging analysis of the scanning electron microstructures with high accuracy. Results from Focused Ion Beam revealed the isotropic growth of intermetallics phases on the plane parallel to interface between steel and Al. Diffusive controlling mechanism was confirmed during the growth of intermetallics phases, a 3D model was derived to find that the growth of the intermetallics phases was dependent on t 0.15 of dipping time.