In recent years, with the rapid development of nanotechnology, the increasing production and application of titanium dioxide nanoparticles (TiO₂NPs) will lead to their release and accumulation in the environment. Owing to that the wetland is located in a relatively lower water catchment environment, TiO₂NPs may enter the wetland ecosystem through multiple pathways, once it enters the wetland ecosystem, it will affect environment and the function of wetland ecosystem and change the process of soil nitrogen transformation inevitably. However, little is known about the effects and mechanism of TiO₂NPs input on the denitrification and nitrous oxide (N₂O) emissions of marsh soil. In this study, in order to explore the effects and its mechanism of TiO₂NPs input on soil denitrification and N₂O emissions, marsh soils were collected from typical field and an indoor cultivated experiment with different addition of TiO₂NPs was conducted, exposure experiments were conducted to investigate the effects of TiO₂NPs (0 mg/kg (CK), 10 mg/kg (A10), 100 mg/kg (A100), 250 mg/kg (A250), and 1000 mg/kg (A1000)) on soil physical and chemical properties, denitrifying enzyme activity, denitrification rate and N₂O emissions of marsh soil. The results showed that (1) all the addition of TiO₂NPs significantly reduced soil pH (P<0.05), the treatments of A10 significantly reduced the content of soil total organic carbon (TOC) (P<0.01), the treatments of A1000 significantly reduced the content of soil nitrate nitrogen (NO₃^--N) and nitrite nitrogen (NO₂^--N) (P<0.05). (2) The addition of TiO₂NPs inhibited the activity of nitrate reductase (NAR) and promoted the activity of nitric oxide (NOR) and nitrous oxide (NOS) (P<0.01), the treatments of A1000 promoted the activity of nitrite reductase (NIR) in initial stage of inhibition, then the trend was opposite (P<0.05), but with the extension of the culture time, the inhibitory effect of TiO₂NPs gradually weakened. (3) The addition of TiO₂NPs significantly inhibited denitrification rate (DNR) and promoted N₂O emissions. (4) DNR was positively correlated with the activity of NIR(P<0.01), N₂O was positively correlated with the activity of NOR(P<0.01). The addition of TiO₂NPs reduced the DNR of marsh soil by inhibiting the activity of NIR, addition of TiO₂NPs improved the N₂O emissions of marsh soil by promoting the activity of NIR. Overall, addition of TiO₂NPs interfered the denitrification process of marsh soil by affecting denitrification reductase activity, resulting in increased N₂O emissions, thus the function of nitrogen source or sink in wetland and global climate will be changed. This study provides a theoretical basis for the assessment of environmental risks of TiO₂NPs input in wetland.