Abstract: Effects of the composition (Cu/Zn and Al) of a Cu-based catalyst for methanol systhesis on its structure and property have been studied. When the aluminium content is fixed at 20.7mol% in a Cu-Zn-Al catalyst for methanol synthesis, the structure of the catalyst precursor kept to be pure FC at Cu/Zn<= 3.6 and maximum activity oi the methanol synthesis will be obtained at Cu/ Zn=1.83. It is thought that the activity ot the catalyst depends highly on the optimum ratio between Cu and ZnO. If the Cu/Zn ratio is fixed at 1.83 with lower Al content, the structure of the precursors will turn out to be a mixing phase of FC and M. The presence of M would have great influence on the structure of FC and on the activity of the catalyst. A good catalyst formula tion(Cu:Zn:Al = 58.5;32.0:9.5) for methanol synthesis can thus be obtained. The role of aluminium is being discussed. Based on the characteristic structure of the paracrystallite, it is suggested that the active center for methanol synthesis is Cu-Zn, where □ is the oxygen vacancy.