It is important to clarify structure of contact between different materials for evaluation of properties of interfaces, which are substantial in electronic devices. Since interaction between different materials has to be evaluated based oil the quantum mechanics, precise simulation of formation process of the contact using ab initio method should be conducted so as to elucidate its structure and properties. In this study, in order to examine structure and strength of Si/Al contact, an ab initio molecular dynamics simulation of deposit of Al atoms onto Si substrate is conducted. Si-(100) surface model with 128 items is introduced and Al atoms are precipitated from above. At first, Al atoms are settled above a ditch between dimer rows of the Si surface and are arranged in a line. After the ditch is filled with the Al atoms, Al atoms are adhered near the line and they construct bonds with each other and with Si atoms in the dimers as well. Consequently, a dense Al layer is formed on the Si surface.