High temperature reduction generally induces the sintering of supported noble metals, therefore resulting in a negative effect on their performance. Here, we show that high temperature reduction was able to dramatically increase the activity of Pd/TiO₂ for ambient HCHO oxidation. We prepared a Pd/TiO₂ catalyst and pre-reduced it with H₂ at low temperature (300 °C) and high temperature (450 °C), respectively, and then tested the activity for HCHO oxidation at ambient temperature. The Pd/TiO₂-450R catalyst showed a much better performance than Pd/TiO₂-300R at room temperature. 100% HCHO conversion could be obtained on the Pd/TiO₂-450R catalyst at a GHSV of 95000 h^-1 and 140 ppm inlet HCHO. The catalysts were then characterized by using Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and other methods. The results indicate that high temperature reduction could induce the strong metal-support interaction (SMSI), decreasing the surface Pd particle size by partially encapsulating and trapping Pd clusters with TiO₂, and also could produce more oxygen vacancies, beneficial to the activation of O₂ and formation of surface OH groups, opening a more effective pathway for ambient HCHO oxidation. Therefore, the Pd/TiO₂-450R catalyst demonstrated high activity for ambient HCHO oxidation.