Abstract: The relationship between the surface acidic and microstructure of gamma-alumina support were studied on three industrial alumina based on the characterizations by XRD，NMR，TEM and pyridine-FTIR. The results show that there are three crystal planes on the surface of alumina: (110)，(100) and (111) planes, and the ratio of the three main planes were different on the alumina supports. The ratios of crystal planes (110)，(100)，(111) on sample alumina-1 ，alumina-2 and alumina-3 are 68%，19%，26%，and 63%，19%，18%，and 59%，19%，22%，respectively. The sample alumina-1 with higher ratio of (110) plane possesses more medium-strong and strong acidity; while the samples alumina-2 and alumina-3 with higher ratio of (100) plane possess more weak acidity.