Nitrogen oxides ( NOx) , as one of the main atmospheric pollutants , seriously affect environmental safety and human health. Selective catalytic reduction ( NH3-SCR ) is the most effective treatment method for NOx removal at present, especially low-temperature SCR denitrification technology, which has very important application prospects and research significance. The research showed that VPO/TiO2 catalyst had excellent low-temperature SCR denitrification activity. The adsorption of NH3 and NO on V2O5 and (VO)2P2O7 surface was simulated by DET, and the reaction mechanism of VPO catalyst was studied at the micro level. The results showed that NH3 exhibited stable chemisorption of Bronsted acid and Lewis acid on the surface of V4P4O22H14 cluster, and the adsorption effect on Bronsted acid sites was more stable. NH3 adsorption effect on the surface of catalyst was excellent because of the hybridization of 2p orbital of N, 2p of O, and 3d electron orbital of V. NO also showed chemisorption on the surface of V4P4O22H14 cluster. Due to the small amount of electron transfer, which was significantly lower than the adsorption energy of NH3, NO could not strongly compete with NH3 molecule. In addition, NO showed stable chemisorption on Brpnsted acid and Lewis acid on the surface of V6O20H10 cluster. The adsorption on Bronsted acid sites was more stable. The E-R mechanism and L-H mechanism of VPO/TiO2 catalyst reaction mechanism were explained.