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This work studied the effect of particle size gradation on the structure and sintering properties of alumina ceramics manufactured by stereolithography after sintering, including room temperature flexural strength, sintering shrinkage, porosity and microstructure morphology. Seven different particle size gradations from coarse to fine were studied, and each particle size gradation was coarse particles: fine particles=6:4. With the increase of the sintering temperature, the degree of sintering and the bonding strength of the interface increased, the shrinkage in all directions, and the bending strength and the closed porosity increased, the open porosity decreased. For the same sintering temperature, the flexural strength and shrinkage in all directions decreased and the open porosity increased with the increase of particle size. The ratio of the height (4mm) shrinkage of each particle size to the length (50mm) shrinkage is about 1.5 times. Due to the presence of the lateral edge resin layer, the width shrinkage of the coarse particles was different from the length shrinkage but closer to the height shrinkage. The width shrinkage gradually approached the length shrinkage as the particle size decreased. When the gradation ratio is the same, and the particle size was ten times different (30μm/5μm, 3μm/0.5μm; 20μm/3μm, 2μm/0.3μm), there was a big difference. When the sintering temperature was above 1500℃, the differences of sintering properties of the comparison groups are 2~10 times. Considering the alumina-based ceramic core, 20/3 has been evaluated comprehensively. It maintains excellent flexural strength and porosity under the condition of slight shrinkage.