Dynamics of Si(100)-oxidation processes at the Si/SiO2 interface and in the SiO2 region are investigated focusing on SiO and Si emissions from the interface and the following incorporation into the SiO 2 and/or substrate. Classical molecular dynamics (MD) simulations with variable charge interatomic potentials are performed to clarify these atomic processes. By incorporating oxygen atoms, two-folded Si atoms are formed after structural relaxation at the interface and are emitted as SiO molecules into SiO2. The energy barrier of the SiO emission is estimated to be 1.20eV on the basis of the enthalpy change in an MD simulation. The emitted SiO molecule is incorporated into the SiO2 network through a Si-O rebonding process with generating an oxygen vacancy. The energy barrier of the SiO incorporation is estimated to be 0.79-0.81eV. The elementary process of oxygen vacancy diffusion leading to the complete SiO incorporation is also simulated, and the energy barriers are found to be relatively small, 0.71-0.79eV. The energy changes of Si emissions into the substrate and SiO 2 are estimated to be 2.97-7.81eV, which are larger than the energy barrier of the SiO emission. This result suggests that, at the ideally flat Si/SiO2 interface, the SiO emission into the SiO2 region occurs prior to the Si emission, which is consistent with previous theoretical and experimental studies. The above mentioned typical atomic processes are successfully extracted from some (or one) of MD simulations among many trials in which a statistical procedure is partly employed. Our results give a unified understanding of Si oxidation processes from an atomistic point of view.