The　leaching　mechanism　of　the　spent　selective　catalytic　reduction　(SCR)　catalyst　was　investigated　by　density　functional　theory　(DFT)　calculations　and　experiments.　Three　models,　namely　V2O5/TiO2,　WO3-V2O5/TiO2,　and　WO3/TiO2,　were　created　to　simulate　the　spent　SCR　catalyst.　Interaction　between　the　surface　clusters　and　the　leaching　agents　of　NaOH,　H2SO4,　HCl　and　HNO3　was　investigated　by　DFT　calculations.　The　adsorption　site　was　determined　through　electrostatic　potential　and　adsorption　energy.　The　calculations　showed　that　NaOH　tended　to　be　adsorbed　on　V　and　W　atoms.　H2SO4,　HCl　and　HNO3　tended　to　be　adsorbed　on　specific　O　atoms.　H2SO4　dissociated　on　all　three　models,　HCl　dissociated　on　V2O5/TiO2　and　WO3-V2O5/TiO2,　while　HNO(3　)dissociated　only　on　V2O5/TiO2.　The　order　of　leaching　ability　among　leaching　agents　was　NaOH　＞　H2SO4　＞　HCl　＞　HNO3.　Ex-periments　showed　that　the　leaching　ratios　of　V　and　W　in　NaOH　solution　were　82.4%　and　54.3%.　In　acid　solution,　the　leaching　ratio　of　V　was　69.0%　for　H2SO4,　52.5%　for　HCl,　and　42.2%　for　HNO3,　while　W　was　hardly　leached　out.　After　acid　leaching,　the　change　in　the　TiO2　lattice　parameter　was　greater　than　that　after　alkaline　leaching.　The　experimental　results　were　found　to　be　consistent　with　the　calculations.