A series of Si-Al based DME synthesis catalysts were prepared by complete liquid-phase method and characterized by in situ XPS, XRD, N-2 adsorption and NH3-TPD analyses. Based on the results, the addition of Si could adjust the pore structure and surface acidity of catalyst, exhibiting a strong promoting effect on the CO conversion and DME selectivity. However, when Si/Al ratio is higher, Si would cover active sites and increase the amount of strong acidity sites, causing the reduction in catalytic activity. It was found from in situ XPS characterization that Cu-0 is the active center of methanol synthesis in DME production, and the addition of Si changes the chemical surroundings of active components and weaken the interaction between Cu, Zn and Al, which maybe give rise to the decrease in catalyst stability. (C) 2010 Elsevier B.V. All rights reserved.