We have investigated the initial oxidation processes on D-terminated Si(100)-2 x 1 and -1 x 1 surfaces and influences of Si-D bonding on SiO2 local bonding structures by high-resolution electron energy loss spectroscopy. It was found from experimental and simulated results that O atoms preferentially adsorb on one of two Si-Si back bonds of a surface Si atom. However, the preferential adsorption on the D-terminated Si(100)-2 x 1 surface is not as significant as the 1 x 1 surface. In addition, from the evaluation by a central-force network model, the length of Si-O bonds formed on the D-terminated 1 x 1 surface is more relaxed than on the 2 x 1 surface. This fact suggests that the existence of Si-Si dimer bonding changes the bonding states of the topmost Si atoms and then the structural change in Si-O-Si formed at the Si back bond occurs.