Formic acid photodegradation is one of the most important reactions in organic pollution control, and helps to improve the hydrogen generation efficiency in titanium dioxide catalyzed water photodecomposition. Based on density functional theory and Reax FF molecular dynamics, the adsorption, diffusion and activation of formic acid on the different anatase TiO_2(101),(001),(010) surfaces are investigated.The result shows that the adsorption of COOH on anatase TiO_2 surface shrinks the energy gap between the dehydrogenation intermediate COOH and HCOO. On the anatase TiO_2(101) surface, the formic acid breaks the O–H bond at the first step with activation energy 0.24 eV, and the consequent break of α-H become much easier with activation energy 0.77 eV. The dissociation of α-H is the determination step of the HCOOH decomposition. Based on density functional theory and Reax FF molecular dynamics, the adsorption, diffusion and activation of formic acid on the different anatase TiO 2 (101), (001), (010) surfaces are investigated. The result shows that the adsorption of COOH on anatase TiO 2 surface shrinks the energy gap between the dehydrogenation intermediate COOH and HCOO. On the anatase TiO 2 (101 ) surface, the formic acid breaks the O-H bond at the first step with activation energy 0.24 eV, and the consequent break of α-H become much easier with activation energy 0.77 eV. The dissociation of α-H is the determination step of the HCOOH decomposition.