In this work, we use ReaxFF molecular dynamics simulations to investigate the interaction between water molecules and silicon surfaces with different orientations under ambient temperatures of 300 and 500 K. We studied the water adsorption and dissociation processes as well as the silicon oxidation process on the Si (100), (110), and (111) surfaces. The simulation results indicate that water can adsorb on the Si surfaces in the forms of molecular adsorption and dissociative adsorption, making the surfaces terminated by H2O, OH, and H species. The molecular adsorption of H2O dominates the (100) and (110) surfaces, whereas the dissociative adsorption dominates the (111) surface. Besides, the adsorbed hydroxyl oxygen can insert into the Si-Si bond of the substrate to make the surface oxidized, forming the Si O Si bonds. Our simulation results also indicate that the (100) surface is mostly terminated by H whereas (111) is mostly terminated by OH. The higher temperature causes more H2O to dissociate and also make all these surfaces more oxidized. Our results are consistent with most experiments. This study sheds lights on the wet oxidation process of Si and Si surface structure evolution in microelectromechanical systems as well as the Si chemical mechanical polishing process.