Syngas　conversion　to　dimethyl　ether　(DME)　is　an　important　reaction　(STD)　in　C1　chemistry　since　DME　not　only　possesses　high　value　but　also　can　be　used　as　a　vital　chemical　intermediate.　Here,　we　design　a　Cu-based　mesoporous　alumina　catalyst　to　realize　the　DME　synthesis　reaction.　It　exhibits　high　catalytic　activity　in　terms　of　CO　conversion　of　21.2%　and　DME　selectivity　of　95.9%　according　to　its　synergistic　effect　between　the　Cu　and　alumina.　In　the　Cu-based　alumina　catalyst,　the　Cu-Cu　bond　is　for　converting　CO　to　methanol　and　the　Cu-Al　bond　is　for　the　formed　methanol　dehydration　to　DME.　Therefore,　the　well-dispersed　Cu　nanoparticles　provide　amounts　of　active　sites　for　methanol　synthesizing,　at　the　same　time　as　the　strong　metal-support　interaction　between　the　Cu　nanoparticles　and　mesoporous　alumina　offering　Cu-Al　active　sites　for　methanol　quick　dehydration　to　DME.　In　addition,　the　mesopores　supplied　by　alumina　support　also　accelerate　the　mass　transfer　and　diffusion,　boosting　the　CO　activation.　This　study　points　out　the　real　active　phase　for　DME　synthesis,　which　plays　an　important　guiding　role　in　design　of　related　catalysts　for　DME　synthesis.　[GRAPHICS]　The　process　of　syngas　conversion　to　DME　over　Cu-based　mesoporous　alumina　catalyst.