The relationship between structure and reactivity plays a dominant role in water dissociation on the various TiOsub.2 crystallines. To observe the adsorption and dissociation behavior of Hsub.2O, the reaction force field (ReaxFF) is used to investigate the dynamic behavior of Hsub.2O on rutile (110) and anatase (101) surfaces in an aqueous environment. Simulation results show that there is a direct proton transfer between the adsorbed Hsub.2O (Hsub.2Osub.ad) and the bridging oxygen (Osub.br) on the rutile (110) surface. Compared with that on the rutile (110) surface, an indirect proton transfer occurs on the anatase (101) surface along the H-bond network from the second layer of water. This different mechanism of water dissociation is determined by the distance between the 5-fold coordinated Ti (Tisub.5c) and Osub.br of the rutile and anatase TiOsub.2 surfaces, resulting in the direct or indirect proton transfer. Additionally, the hydrogen bond (H-bond) network plays a crucial role in the adsorption and dissociation of Hsub.2O on the TiOsub.2 surface. To describe interfacial water structures between TiOsub.2 and bulk water, the double-layer model is proposed. The first layer is the dissociated Hsub.2O on the rutile (110) and anatase (101) surfaces. The second layer forms an ordered water structure adsorbed to the surface Osub.br or terminal OH group through strong hydrogen bonding (H-bonding). Affected by the H-bond network, the Hsub.2O dissociation on the rutile (110) surface is inhibited but that on the anatase (101) surface is promoted.