Rutile TiO<sub>2</sub> (110) surface has been studied as the ideal model catalyst system, formaldehyde has been reported as the most important intermediate of the catalytic reaction. Therefore, it is necessary to establish a clear picture of the diffusion process at the molecular level about formaldehyde on the rutile TiO<sub>2</sub> (110) surface. In this work, we firstly reported that formaldehyde molecule can stride the O<sub>br</sub> row and adsorb on the neighbored Ti<sub>5c</sub> row assisted by one adjacent hydrogen atom, in addition that increasing of localized H atom adjacent to formaldehyde molecule can enhance the probability of diffusion and desorption during laser irradiation. The theoretical calculation showed that the existence of hydrogen bond of BBOH-OCH<sub>2</sub> can reduce the barrier of the diffusion of formaldehyde perpendicular to the rows of O<sub>br</sub> rows and generally enhance the probability of both diffusion and desorption. These results provided powerful evidence about the 2D diffusion of formaldehyde on TiO<sub>2</sub> surface which is helpful for investigating the mechanism of photo-catalytic.