Theoretical　simulation　of　the　adsorption　and　dissociation　of　two　NO　molecules　at　the　Cu2+,　Cr3+　and　bridge　Cr3+　sites　(b-Cr3+)　on　the　normal　spinel　CuCr2O4　(100)　surface　has　been　carried　out　by　density　functional　theory　calculations.　The　results　show　that　the　formed　N-down　and　O-down　NO　dimers　are　negatively　charged.　The　formation　of　stable　O-down　dimers　on　the　surface　leads　to　the　great　elongation　of　N-O　bond,　which　contributes　to　the　NO　reduction.　The　transition-state　calculations　indicate　that　the　decomposition　of　O-down　NO　dimer　at　the　b-Cr3+　site　is　most　favorable　and　N2O　is　the　major　reduction　product.