The submicron Al2O3 composite powder was obtained by sand milling process, which was used to prepare fine grained Al2O3 ceramic substrates. The effect of slurry composition on rheological properties of slurry, bulk density and stress-strain behavior of green tape was investigated, and the influence of sintering schedule on average grain size and flexural strength of ceramic substrate was also studied. The results show that key factors such as solid content, R value (mass ratio of plasticizer to binder) and dispersant dosage determine the rheological properties of slurry. The increase of R value leads to the reduction of tensile strength and density of green tape, and the increase of solid content is beneficial to increase the possible maximum casting thickness. Under the optimized process conditions, 0.16~1.20 mm green sheets can be prepared. At a sintering temperature of 1 550 ℃, a heating rate of 2.5 ℃/min and a holding time of 60 min, the average grain size of the prepared ceramic substrate is about 1.1 μm, the grain size distribution is uniform, and the flexural strength reaches (440±25) MPa.