Effects　of　hydrothermal　aging　at　80　and　850　degrees　C　on　catalytic　performance　and　stability　of　Cu/SAPO-34　catalysts　with　different　Cu　loadings　were　examined,　and　their　catalytic　activities　were　investigated　for　the　selective　catalytic　reduction　(SCR)　of　NOx　with　ammonia.　Over　the　fresh　catalysts,　the　NH3-SCR　activity　increased　with　the　loading　of　copper　in　the　low-temperature　range　and　decreased　in　the　high-temperature　range.　Both　of　the　isolated　Cu2+　ions　and　CuO　synergistically　influenced　the　SCR　behavior　of　the　Cu/SAPO-34　catalysts,　which　gave　rise　to　the　distinct　trends　of　catalytic　activity　in　the　two　temperature　ranges.　Structural　damage　and　dealumination,　however,　were　observed　in　the　aged　samples,　leading　to　a　severely　decreased　amount　in　acid　site　and　a　loss　in　crystallinity.　After　hydrothermal　aging　at　850　degrees　C,　there　was　some　aggregation　in　Cu　species　and　the　redox　capacity　of　the　0.8Cu/SAPO-34-850　catalyst　was　improved.　It　is　found　that　the　isolated　Cu2+　ions　were　transformed　into　the　Cu-AlOx　species　after　hydrothermal　aging　at　80　degrees　C.　These　results　clearly　demonstrate　that　the　change　in　the　state　of　copper　species　and　the　damage　in　structure　led　to　different　catalytic　activity　of　the　sample.